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Oral History Transcript — Dr. Charles Slichter

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Interview with Dr. Charles Slichter
By Babak Ashrafi
At University of Illinois, Physics Department, Urbana, Illinois
March 26, 2005

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Charles Slichter; March 26, 2005

ABSTRACT: Topics discussed include: Harvard education, war work at Woods Hole, research with Edward Purcell, University of Illinois, Albert Overhauser, superconductivity, Kondo effect, President's Science Advisory Committee, teaching, consulting, computing, John Bardeen, Wheeler Loomis, David Pines, Fred Seitz and Edward van Vleck.

Transcript

Slichter:

So, is this table convenient for you?

Ashrafi:

Sure.

Slichter:

Would you rather that chair or this one?

Ashrafi:

Iím good here.

Slichter:

Good.

Ashrafi:

So today is March 26, and this is Babak Ashrafi in Professor Charles Slichterís office in Urbana. And, what we usually do is try to get a background.

Slichter:

Right.

Ashrafi:

Your family background, your educational background, —

Slichter:

Yeah.

Ashrafi:

— and then step our way, as much as —

Slichter:

All right.

Ashrafi:

— we can through your career, which is both scientific and institutional, and intellectual, all of the aspects that we can.

Slichter:

Good.

Ashrafi:

So, were your parents, were they...?

Slichter:

My mother and father are Midwesterners. My father grew up in Madison, Wisconsin. His dad was a professor of mathematics, and later dean of the graduate school.

Ashrafi:

Okay.

Slichter:

And, my motherís father, my motherís father went to the University of Illinois, and then — his field was railway engineering. And, he lived here, and then he was on the faculty at Purdue, and then he moved to Wisconsin, where he was on the faculty. And then, he left that to be a consulting engineer.

Ashrafi:

Uhm-hmm.

Slichter:

And, my parents met in Madison. My dad got a PhD in economics at the University of Chicago, and then started his academic career at Princeton, moved to Cornell, and then in 1930 moved to Harvard. And, he was initially a professor in Harvard Business School and then became a professor of economics, also, and he was one of the first people to hold the position of university professor, which was a special professorship that Harvard established. And, his field was labor economics and public policy. So, I grew up in — I was born in Ithaca, New York while my parents were at Cornell, in 1924, January 21, 1924. And, then we moved to Cambridge. I went to the Buckingham School from first grade through fifth grade, which where they had boys and girls. It was a girls school beyond that. Then, I transferred to the Brown & Nichols School, which was a boys school.

Ashrafi:

Uhm-hmm.

Slichter:

And, I graduated from there in 1941. My, I have a brother who graduated a year ahead of me. And, the, we spent, we, my parents had a summer home in Madison, Wisconsin. And so, every summer while I was growing up we spent the summers on the north shore of Lake Mendota, where we had a summer home right immediately next door to my fatherís parents. And so, I really have quite strong Midwestern roots. The part of the family history which is interesting, because of things which come later, is that when my grandfather, my fatherís father — Iím named after him. He was also Charles Slichter, but Charles Sumner Slichter — and, he, when he became head of the math department the first thing he did was to hire a very famous pure mathematician. His, he was, my grandfatherís field is applied math. He didnít have a PhD, but he hired a very eminent mathematician named Van Vleck. And, after whom now the math building is named, at the University of Wisconsin. TheÖ

Ashrafi:

Is he related to the physicist?

Slichter:

Heís the father —

Ashrafi:

Okay.

Slichter:

— of that physicist. And, that father was my undergraduate advisor.

Ashrafi:

Uh huh. Yes.

Slichter:

I mean the son, the son.

Ashrafi:

Yes.

Slichter:

The physicist was my undergraduate advisor.

Ashrafi:

Can I ask you about the early schools you went to in Cambridge? What kind of schools were they?

Slichter:

Well, the Buckingham School was a, was a private school. And, Cambridge public schools were terrible. And, there was a lot of politics involved, evidently, and appointments of people. And, so my parents just put me and my brother in the Buckingham School, which was, you know, just a very fine school. The, later Buckingham and Brown & Nichols merged. I mean, in recent years, you know. That might have been the seventies, or something like that.

Ashrafi:

And was it, was it kind of a general education you might expect, or was there a particular emphasis?

Slichter:

No. It was completely standard type of education. For example, at — well, in the Buckingham School, you know, we had basically the standard things. I donít remember whether we had foreign language there, but probably not. But you know, English, math, so on.

Ashrafi:

Do you remember how much math and science you had?

Slichter:

Oh, I just had the standard things. And, you know, and then, then when I went to Brown & Nichols why, again, this was classic education. I had — but I had, but a really good one. For example, in Brown & Nichols, in the sixth and seventh grade there in their under, lower school, why my English teacher was a, was a writer of boys stories.

Ashrafi:

Uh huh.

Slichter:

And, he just got us terrifically interested in reading books. You know, I mean we would, we would, he kept track of books that we read, and we had a competition who was going to read the most books. And, the, and one result of this was that I became a very good reader. I read very fast. And, this was just, I mean, this was just classic belief in the importance of English. And, in the upper school we had to write a theme a week, which I hated, because I never had, you know, I never really had things I wanted to write about. Well, nevertheless, we had to write. And, but I, you know, it gave me a lot of practice. And so, I certainly knew all about grammar and things like that. The math courses were quite the normal things. I didnít have calculus in high school. I had, you know, geometry and algebra. And, when I got to college, why I took the beginning analytic geometry and calculus course. My freshman year in college I found myself in the beginning physics course —

Ashrafi:

Uhm-hmm.

Slichter:

— sitting next to Roy Glauber, who is the theorist at Harvard. And, Roy let me know that he was taking third-year calculus. But, fortunately, I didnít let that scare me out of it.

Ashrafi:

How much science did you have before college?

Slichter:

Well, I had never had a chemistry course. I had sort of a general biology thing, which I disliked. We had sort of a general science thing, which has some astronomy in it. But, in my senior year I took a physics course which was taught by a man who was actually a professor at Boston University. And, but came over and taught this course. And, I just absolutely loved it.

Ashrafi:

Do you remember his name?

Slichter:

His name was Stratton. And, one of the recent issues of the Brown & Nichols alumni magazine has a picture of him, but they donít have his name under it. So I wrote them to tell them that was a great pity because he was such a wonderful, wonderful man. You know, he would, but one of the things he did, in class, he would give us little problems and then you would, which weíd then sit and work. And, as soon as we thought we had the solution weíd take them up to him, and if they were correct he had a big blue pencil, so heíd put a blue check on it. And so, I mean this was, getting your blue check was something that you prized. But, you know, this was not, this wasnít about atomic physics, and stuff like that. This was falling bodies. And, you know just, a very unsophisticated physics course. But, what I loved about it was that you learned a few principles and then you applied them to solve problems. And, I loved the fact that you used math in it. And, you know, again, I had very conventional math courses, you know, but I just absolutely loved geometry. And, you know, thereís, I think thereís a, I got a terrific lift out of the fact that I could really do science easily, and just, you know, I could thrive as doing it, and stand out in the class. Whereas in history, for example, I just have a terrible memory for things like that. And, I remember things in an impressionistic manner, not sort of in a, with great detail. So, you know, I would realize I didnít know the name of a person. I knew what he — when I was trying to think of, you know, recall on exams. But, I had wonderful history teachers. I mean, we had, we didnít have any multiple choice, or stuff like this, you know. You had an exam. Our exam, or the final exams, why they were these things where, ďDiscuss this statement,Ē or something like this, where you had to write out a — I mean, we were trained to make a brief outline of the points you wanted to make, and then, and then write it.

Ashrafi:

Uhm-hmm.

Slichter:

So, you know, over on the left hand side of the blue book youíd have, youíd put down some stuff. And so, it was really, I mean it was; it was a terrific education.

Ashrafi:

Sounds like it, yeah.

Slichter:

And so, but I knew enough not to take any history when I got in college. [Laugh] My freshman advisor wanted me to take all the standard stuff, you know, like I was still in Brown & Nichols. But, I wanted to get going in math and science.

Ashrafi:

So, you went to Harvard knowing you were going to do math and science?

Slichter:

Oh yeah. Knowing I wanted to do physics.

Ashrafi:

And, was this because of the senior year high school course?

Slichter:

Yes. It was. And, I always knew I wanted to do science. I was, you know, and itís interesting, although my father was an economist, both my mother and father always encouraged my brother and me in, you know, in science. And, they sort of held up our grandfathers as, —

Ashrafi:

Hmm.

Slichter:

— as examples to us, you know, of people who loved those fields.

Ashrafi:

Was there much discussion about why science, as opposed to economics?

Slichter:

You know, it never occurred to me that Iíd go into economics.

Ashrafi:

Uhm-hmm. But, do you know

Slichter:

No, no there wasnít.

Ashrafi:

Uhm-hmm.

Slichter:

And just that — my parents were supporters of our enthusiasms.

Ashrafi:

Uhm-hmm.

Slichter:

And, so I never felt that, I never had to explain to them why I wanted to do it, and they didnít urge me to do it.

Ashrafi:

Okay.

Slichter:

I just, you know...

Ashrafi:

And you said you had one, you had one brother?

Slichter:

Yes. He was, heís no longer living. He got a very virulent form of throat cancer about fifteen years ago.

Ashrafi:

And did he...?

Slichter:

But he was a, he majored in chemistry. He started out planning to go into biology, and then switched to chemistry. And, he got a PhD in physical chemistry with George Kistiakowsky at Harvard.

Ashrafi:

Oh. Yeah.

Slichter:

And then he went to Bell Labs, and he spent a career there and became a manager. He got up to the level of so-called ďexecutive director,Ē which is the level just below vice president.

Ashrafi:

Any other siblings?

Slichter:

No.

Ashrafi:

Was there much discussion, or not, about going to Harvard or elsewhere?

Slichter:

Well, when I was trying to decide where to go to college, I was strongly drawn to Wisconsin, and to Harvard. The Wisconsin thing, however, was, I think there were two elements there. The first one is, you know, I had wonderful associations with Madison, and the University of Wisconsin, both because of my family and because of, you know, this is our summer home. And, both my mother and father went there. All of my fatherís—my father had three brothers who went there. One of them was an incidentally geophysicist, who was Louis Slichter, who was head of the Geophysics Institute at University of California. The building, the space sciences building, is named after him, —

Ashrafi:

Oh.

Slichter:

— at UCLA. The — and but the other thing was, I was enamored with a young lady who I had met during the summers, who was going to go there. And so this had a sort of personal thing. And so, I wondered about this. And, I had a French teacher, at Brown & Nichols, who said to me, ďWell, Charlie,Ē he said, ďYou know, you can go Wisconsin or you can go to Harvard.Ē He says, ďIf you go to Wisconsin, for the rest of your life youíll be telling people you could have gone to Harvard.Ē [Laugh] Which, so, you know, I really realized that going to Harvard was probably the sensible thing to do, so thatís what I did. You know, my parents didnít like stuffed shirts, and people who were stuck on themselves. And, and so, and I didnít have a sort of sense of awe of Harvard. I mean, they enabled my brother and me to believe that the Harvard faculty are, you know, theyíre ordinary faculty members, like faculty members at other places. There wasnít something about them which made them a really different breed, and that Harvard had its good people and its people who werenít so good. And so, it wasnít sort of perfection. But.

Ashrafi:

So, you werenít intimidated?

Slichter:

No. I wasnít intimidated. I mean, it was a lucky thing because I might have been intimidated by meeting people like Roy Glauber. Anyway, so just after I graduated from Brown & Nichols, that summer my father was teaching summer school at Stanford. And, my brother and I, this is the summer of Ď41, my brother and I drove our parentsí car out to the West Coast, and then I went to summer school at Berkeley, —

Ashrafi:

Oh.

Slichter:

— and stayed in the International House, and took swimming and chemistry. Itís the only chemistry course Iíve ever had in my life. And, I had a really great time. And, one of my great loves is jazz. And there was a wonderful jazz band that was performing out there, Lou Waters and his Yerba Buena jazz band, named after Yerba Buena Island. And, I was introduced to them by some of the older guys who were living there at the International House, and we went into San Francisco to hear them. So, and that, so this was a terrific experience. Anyway, so September Ď41 I entered college, and of course in December was Pearl Harbor.

Ashrafi:

So, youíre seventeen?

Slichter:

Yeah.

Ashrafi:

So, that was a little early. Did you skip some period? Since you...?

Slichter:

Well, actually, I started first grade in Washington, in 1929. And, my father was there working at the Brookings Institution. He had took a couple of years leave from Cornell to be in Washington. And, but I had trouble seeing. They didnít, at that point, they didnít realize I needed glasses. And, I think I started, the way the age things went, I started in the middle of the year, something like January for the, you know, sort of the spring semester. And, I really had trouble seeing. And, they realized this. And, so since it was only a few months before we were going to go out to Madison, where they had their doctors, they decided to pull me out. So, I got glasses, and then I went into the Buckingham School, and I had a lot of trouble learning to read. The other kids in the class were learning much faster than me. And, but there was a young woman who was an assistant to the teacher, and she knew about phonics. And, she took me aside and gave, and explained phonics to me. And, as soon as I had a, understood the logic of reading why I very quickly learned it. And then, then they had what they called the ďfree class,Ē which was between the second and third grades. And, so you basically doing the second and third grades in one year. So, from the first grade I went into that. And then, but I really, so I skipped a grade, but I probably, if, I would have been the same age if I hadnít. I had to skip a grade to make up for the fact that I got pulled out.

Ashrafi:

Okay. So, you go to Harvard in the fall of Ď41?

Slichter:

Right. And, you know, at that time Harvard had a two-year elementary physics course.

Ashrafi:

Uh huh.

Slichter:

And, I had Wendell Furry as the professor. But, with Pearl Harbor, they realized that we shouldnít be going through college slowly, so they converted it to a one-year course. And, in the spring they gave of us some E & M. And then there was a, I used to, they had an intermediate level E & M course, which ordinarily youíd take as a junior. But, I took it that summer. And, I guess I took a, I probably took a math class. And, yes. I did. I took math and that. And then, in my, so the start of my sophomore year, I was eligible to start taking the electronics courses. So, I took two electronics courses in the fall and in the spring. And, that was most of what Harvard taught in electronics.

Ashrafi:

Okay.

Slichter:

And, the, most, many of the graduate students had left, so I was hired to grade lab reports in the E & M course I had taken that summer. And the professor in the course was Van Vleck.

Ashrafi:

Uh huh.

Slichter:

And, so he actually, so he became my advisor. And, I worked for him.

Ashrafi:

Worked for him doing...?

Slichter:

Grading lab reports.

Ashrafi:

Okay.

Slichter:

One of the people I had was — so, I was grading lab reports for those of my classmates who hadnít taken the course in the summer. And, this was kind of what the war was like. One of the people I had was Fred, Freddie de Hoffman. I donít know whether that name means anything to you or not, but he became a big shot at, in — what is the company? General Dynamics, I think. Anyway, I felt that I probably shouldnít stay in college with the war on. And, I went to Van Vleck and I said to him that I thought I should enlist, and should I list in the Signal Corp or something like this. And he said, ďWell no. You really should try to go on a war project. They need scientists.Ē And he suggested that I call E. Bright Wilson, who was a physical chemist.

Ashrafi:

Uhm-hmm.

Slichter:

The father, you know, of the Wilson, Nobel Laureate.

Ashrafi:

Yes. Okay.

Slichter:

And, so I got an appointment to see him, and went and had an interview. And, so I had, letís see, so I guess I was at that stage. I had just turned nineteen. My birthday was in January. Anyway, then I didnít hear anything from him. And, some weeks went by, and Van Vleck stopped me one day and asked me, what had happened in that. And I said, ďWell, I hadnít heard anything back.Ē And, two days later I got a phone call from Wilson. So, itís obvious that Van — well, I think two things happened. One was that Wilson couldnít find someone, and the second thing was Van called him again. Anyway, Wilson...

Ashrafi:

This is in —

Slichter:

Had itÖ

Ashrafi:

— Ď43?

Slichter:

Excuse me?

Ashrafi:

This is in Ď43?

Slichter:

This is Ď43. Yeah. So, Wilson was head of a war project at Woods Hole, Mass, which there were actually two projects there. One of them was studying underwater explosives, and the other was studying air blasts. And, this was part of the NDRC activity. So, in June, I guess, of Ď43 I went down to Woods Hole, where I worked in electronics. And, I was there until the war was over.

Ashrafi:

Okay.

Slichter:

And, of course, the Japanese surrender was in August — and, I realize I wore the wrong hat today, because I have a wonderful Woods Hole Oceanographic cap, which has a picture of the Atlantis on it, their sailboat, which where we did, which we used for some of the work we did.

Ashrafi:

Who else was at Woods Hole then?

Slichter:

Well, letís seen. Don Hornig, and — these were all physical chemists. And George Frankel. I donít know whether that means — Don Hornig, of course, later became the presidentís science advisor. And, letís see, Paul Cross, who was a physical chemist. Bill Schneider, a Canadian, who was very prominent in the National, Canadian National Research Council researches. And, letís see, who else? Well, Bob Cole, who was a physicist, who was, who later became in the chemistry department at Brown University. Quite well known in the field of dielectrics, and things. The so-called Cole Cole Plot, of Bob Cole and his brother. And, Bob Cole — my immediate boss was a guy named Dave Stacey, who was a Harvard undergraduate, who knew electronics. And, a fascinating guy. He was a, just before coming to Woods Hole, he had been teaching glider flying to the Army. He was a self-taught flyer. And, as he was my, he was in the lab. He was my boss. He didnít have a graduate degree, but he knew a lot of electronics. He got a PhD after the war, at Colorado, and his boss was Bob Cole. Bob Cole was the only person to do an experimental thesis with Van Vleck. And, just one of these, it was my introduction to a style of doing physics, which Purcell also had, which was the capacity to take really complex things and understand them, and translate them into very simple discussions, which cut away stuff that you didnít need, and focused on — you know, he could find an example where by rather elementary means you could work out what was happening. And, he was, he was just a terrific combination of experimenter and theorist.

Ashrafi:

This is Cole, now?

Slichter:

This is Cole?

Ashrafi:

And, you learned this method from him?

Slichter:

Well, I first saw this with him, saw him doing this. And, I mean it was, I just, I was so deeply impressed, and it was, you know the theory — there was some very powerful people doing theory in connection with these underwater explosives. Not on our project, but in other places. And, I think Lars Onsager did some. But, people of this caliber. And, Bob Cole could read these papers and understand them, you know. Now, you understand, I knew very little physics.

Ashrafi:

Yeah. Just the E & M that you described?

Slichter:

Yeah, I mean I, I hadnít had mechanics beyond the elementary course. Iíd had, by then Iíd had the equivalent of three years of calculus, —

Ashrafi:

Uhm-hmm.

Slichter:

— you know, put together with my freshman year as a summer school, and my sophomore [Laugh] year. So, I was catching up. ButÖ

Ashrafi:

Can you give me an example, or would you tell description of this method of physics that you described?

Slichter:

Uhm, letís see. Well, itís basically this, thatÖ well, let me think about that, —

Ashrafi:

Okay.

Slichter:

— and I think I can probablyÖ

Ashrafi:

Is there some reason that you...?

Slichter:

Well let me give you, hereís an example. I mean, the, in magnetic resonance thereís a.

Ashrafi:

But, I mean from Cole at this time?

Slichter:

From Cole? No. I canít give you an —

Ashrafi:

Okay.

Slichter:

— example from Cole, other, — but I mean, one of the things that — no, I guess I donít, I canít remember an example to give you. ButÖ

Ashrafi:

You were saying any time thereís a theoretical issueÖ

Slichter:

An issue. He had the capacity of explaining it with such clarity that it seemed very simple. You know this is, Fermi is a famous exponent for being able to do this.

Ashrafi:

Uhm-hmm.

Slichter:

So itís, if youíre familiar with sort of what people say about him, this is like that. And, Purcell is the same way.

Ashrafi:

And, was this something that you recall taking away from Woods Hole?

Slichter:

Oh yeah.

Ashrafi:

Okay.

Slichter:

Absolutely.

Ashrafi:

Anything else that you felt taking away from Woods Hole this year?

Slichter:

Well, one of the things I took away from Woods Hole, was a recognition that these physical chemists knew all the physics that the physicists knew, and in addition to that they knew chemistry. And, now this is very much these Harvard physical chemists. And there are other places where they are like that. Thereís, that tradition is at Berkeley, and also at Caltech, and also at Cornell. I mean I sort of learned that, subsequently, you know, that itís at all of these places. But, I donít know, thereís a, you know — an example is, you know, thereís a quantum mechanics textbook, Pauling and Wilson, —

Ashrafi:

Uhm-hmm.

Slichter:

— which, you know, E. Bright Wilson wrote with Linus Pauling. And, I mean, itís, you know, itís, itís a very sophisticated book, certainly, for chemists.

Ashrafi:

Uhm-hmm.

Slichter:

And, itís a good elementary quantum mechanics text for physicists. But, I mean, you know, itís outdated now. Thereís a lot thatís happened since then. But, still actually stands up. And, all those people knew quantum mechanics, you know, were very fluent in using it.

Ashrafi:

Was Ken Wilson around?

Slichter:

He was a child. And, I donít remember [Bell rings] him, in those days, but I remember seeing Bright Wilsonís family, because they were all living down there. He had quite a few children, but they were small.

Ashrafi:

So, you went back to Harvard in...?

Slichter:

So, I went back to Harvard in — well, I realized that I didnít make the start the fall semester, so I was going to have to come back at mid-years, of 1946, come back in January. And so, of course a lot of courses start in fall, and are two-semester courses. And so, I went and talked with Van Vleck about what to take. And, he said, well, he was teaching a mechanics course, intermediate level mechanics, and I could take that, but I should work up the first half of it. And, he had a set of review questions, and things, and he told me the text book. So, that fall in Woods Hole, why I worked through the chapters of that book.

Ashrafi:

What book?

Slichter:

Singe and Griffiths, which was an excellent book.

Ashrafi:

Okay.

Slichter:

But, this just was the most wonderful experience for me, because I was by myself. There was no one whom I could ask question of. And he told me I should be sure to do the homework problems, which were in the book. And, I was by myself, and if I tried to do a homework problem, and I couldnít do it, I just had to go back into the book and dig and see that what was it that I was missing that made it so I couldnít do this. And, I really, this is where I really learned how to study physics. And, you know, before I went down to Woods Hole, I would get on an examination and a question would come up which would really surprise me. And, that never happened again. And, itís, I just really learned how to study physics. And, it made a tremendous effect on my, on my ability as a student. And, you know, what I got out of the courses. And, that doesnít mean that, you know, that I got everything there was to get out of a course, but I really didnít — I mean I, I suppose itís all right to say this, but I mean I just would write perfect exams. And, you know, anyway, it was a terrific experience.

Ashrafi:

Did you write perfect exams before this experience?

Slichter:

No. No. No.

Ashrafi:

Okay.

Slichter:

No. That was my point to that.

Ashrafi:

Okay.

Slichter:

Itís because I, because I learned to not be satisfied. You know, previously, I got stuck on a problem, Iíd try to get someone to help me, you know, and weíd talk about it. And, I remember doing this in freshman year, in that physics course which was a tough course. And, there was a graduate student in physics who was proctor on our entry way, and we would go to see him. Dick Brown, who lived next door, was a physics major, and he and I would, you know, if we got stuck weíd see if we could figure it out, and then weíd go up and see Eisenstein, and then he would help us. But, you know, the trouble with that is, you see, I didnít, hadnít figured it out myself.

Ashrafi:

Uhm-hmm.

Slichter:

So, I didnít have the understanding of it that I got from this experience getting ready to take Van Vleckís course. AndÖ

Ashrafi:

So, when you came back, you took mechanics?

Slichter:

So, I came back and I took mechanics. And, letís see, what did I take? I took another — I guess I took a mathematical physics course. And, then I, they gave me some credit toward graduation from my Woods Hole time. I took a course in psychology, and I took an economics course. And, I just loved that economics course. And, I, and I really excelled in it. And, I realized that if Iíd taken economics earlier, I would have taken more of it. But, that summer, I needed to go to summer school to graduate, and that summer Sam Goudschmidt was coming to teach at Harvard. And, he taught two courses, and I wanted to take them, but I hadnít satisfied the requirements in the social sciences at Harvard, and I needed to take another economics course, or something like that, to satisfy them. And, I talked to Van Vleck about it, and he really realized, you know, it was crazy for me not to take the courses that Goudschmidt was teaching. And so, he wrote a letter to Harvard, urging them to permit me to reduce the economics requirement on the basis of the fact that I probably heard a lot of economics discussed over the family dinner table for many years, and they did that. So, at the end of that summer I graduated.

Ashrafi:

So, what were Goudschmidtís courses?

Slichter:

Letís see. I think one of them was an optics course, and the other was an advanced dynamics course. Itís basically the course that Goldsteinís mechanicís text is — I mean, itís Hamiltonians. So, we had, in Vanís course, we had Lagrangianís, and did that, but we didnít deal with Hamiltonians, and so on. But this was sort of the formal course preparing you for basically the classical mechanics background on the quantum mechanics.

Ashrafi:

And, you had no quantum mechanics other than Lagrangian?

Slichter:

No. I had none as an undergraduate.

Ashrafi:

And, was that typical?

Slichter:

Yeah.

Ashrafi:

Were you ever tempted by physical chemistry?

Slichter:

No.

Ashrafi:

How about economics?

Slichter:

No. No. No. It was, I was, I enjoyed it, and, but no Iíve always just loved — physics was the thing. And, as I said, I only took that one chemistry course in summer school, and that was not a, that was, that was really a high-grade high school course. I mean, you know, I did well in it. And, it was the sorts of things like the gas laws and stuff like this that physicists eat up, and the chemists were struggling with. So, you know, I had a, you know, I had a good time in it because I got the pleasure out of being able to know, to deal with things that some of the other students had trouble with. And, I mean, that cheers you up, and makes you feel that youíre not a hacker. And so, that, that was, it was a very really nice experience. And you know, Iíve always loved to help others, and sort of teach them. So, I had some of that experience in that course, but I didnít know much chemistry.

Ashrafi:

Was there much of thinking about where to go for graduate school?

Slichter:

Yeah. I had the feeling that I ought to go someplace else, —

Ashrafi:

Okay.

Slichter:

— because I thought that was sort of tradition. And, as I said, Van Vleck was my advisor, and now you think of the timing of this. January 1946 is when the Purcell, Pound, and Torrey Physical Review letter announcing the discovery of nuclear magnetic resonance was published. But, I didnít know about this. And, I mean I was focused on my courses, and I was still an undergraduate. And, Van would, often as we would come to the end of the class, he would say to me, ďHave you, how are you coming on your thinking about where you want to go to graduate school?Ē And I said, ďWell, I still havenít made up my mind.Ē I hadnít, I had applied to Illinois, Wisconsin, Minnesota, Cornell. I wrote a letter to Princeton, to apply to Princeton, and I got back, you know, asking for application materials, and I got a letter back from them saying, ďItís very difficult to get into Princeton.Ē And, then they didnít send me the materials. And, basically, sort of challenging me to see, if I really wanted to go there I would come back and try to insist on getting in. So, I just thought, and said, ďThe hell with them.Ē [Laugh] And, but, you know, I was offered assistantships at all of these places. I mean they were, every place was desperate, because there were all these students coming back from the military, in addition to the usual people. So, all of these places [ringing bell] were scrambling to have teaching assistants, and so on. And, you know, Iíd had war experience, so.

Ashrafi:

Did you mention Harvard in that list?

Slichter:

No. But, Vanís, Van kept saying, he said, ďBut donít overlook Harvard.Ē He said, ďYou really should go to Harvard.Ē And, he told me, he said, ďLook,Ē he said, ďOther people, you know, if theyíd just gone to the same place, thatís one thing.Ē He said, ďBut, you know, your family is from Wisconsin, and so you have that outlook, and youíve been off in the war.Ē He really wanted me to go to Harvard.

Ashrafi:

Uhm-hmm.

Slichter:

And, so I decided to go to Harvard, and I applied and got in. And, then in my first year in graduate school, he stopped me in the hall one day and said to me, ďYou know, you should really do your thesis with Purcell. And it would be great to look at electron spin resonance of paramagnetic ions.Ē Well, I didnít know what a spin resonance was. I didnít know anything about paramagnetic ions and stuff like this, but you know Van Vleck had done a lot of the theory of paramagnetic ions, —

Ashrafi:

Yeah.

Slichter:

— and crystal field levels, and things like this. And, Harvard — and you know, nuclear — everyone in — you know, Purcell was doing nuclear magnetic resonance, but not electron spin resonance. And, of course, to study these materials for which Van Vleck had done so much work, you want an electron spin resonance. So, he wanted to launch electron spin resonance studies. And, you know, itís very interesting. Itís clear he wanted me to be an experimenter and not a theorist. And, I think he just felt that theory is a really cut-throat activity. You know, let me come back just a second. You know, in Madison, at the University of Wisconsin, my — so my grandfather hired Van Vleckís father, so my, the Slichter family knew the Van Vlecks. And Van was somewhat younger than my father. But, they lived down the street, and so my parents knew him, and he was, my father knew him when he was growing up, you know. And, they had a great love of Wisconsin. My dad actually kept his watch on Madison time.

Ashrafi:

[Laugh] Is that right?

Slichter:

Yeah. And, the, of course another family that was there were the Bardeens. And, Johnís father was the dean of the medical school. And, theyÖ

Ashrafi:

By ďthereĒ you mean Wisconsin?

Slichter:

At Wisconsin. Yeah. So, you know, Van went and attended the University of Wisconsin, and then he came to Harvard and got his PhD, in two years. And, then, including taking a course about railways in the business school. And then, he went out to the University of Minnesota, on a faculty position. Thatís where he met his wife, who was a librarian there. They got married. And then he was hired by the University of Wisconsin. And so, he was teaching at the University of Wisconsin when Bardeen, who was an undergraduate there, and majoring in electrical engineering, took some courses from Van. And, so thatís, you know, that was really, thatís the origin of their interaction, which I donít know whether youíve, to what extent youíve followed Bardeenís career, etcetera, and but Van Vleck played a significant role in his career. I mean the physicist Van Vleck. And, anyway, so my family, my parents were personal friends of the Van Vlecks.

Ashrafi:

Okay.

Slichter:

And...

Ashrafi:

So, he took an interest in you?

Slichter:

And, yeah. I mean he really, but he took an interest in lots of students, you know. But, and he was just, Van Vleck is a really sweet person. But, you know, he would say, ďWell, why donít you come around and weíll talk about it.Ē And then Iíd come around to his office and he would say, ďWell, now what did you want to see me about?Ē [Laugh] I mean heís, he was, heís really a very unusual sort of person. But, my belief is that he wanted me to work with Purcell, which was why he urged me to stay on.

Ashrafi:

Did you start research pretty early on? Did you have a period of taking some courses before you started research?

Slichter:

Well, I took courses my first year, and I started research that summer.

Ashrafi:

Okay. What were the courses?

Slichter:

Well, I started taking quantum mechanics, and letís see, what else did I take?

Ashrafi:

Who taught quantum mechanics?

Slichter:

Wendell Furry. And, I, letís see, what else? Oh, I took a, an atomic physics course, which was sort of the, telling you the, oh, the background to quantum mechanics, and Bohr theory, and stuff like this. And, that was taught by R. R. Wilson, who spent that, Iím not sure whether it was just the fall semester or the whole year, at Harvard. You know, Van Vleck was the chairman of the physics department right after the war. And, they set up a committee to make a recommendation for the — they asked the committee to recommend the five most outstanding young physicists. And, that committee recommended R.R. Wilson, Ed Purcell, Norman Ramsey, Julian Schwinger, and Feynman. And, Harvard had them all, except for Feynman. And, but you have to, I donít know what it was about Harvard, but Wilson, I guess, wanted to leave and went to Cornell. And, but I had him when he was there. And then I took a course from Ken Bainbridge, I guess, a nuclear physics course. And, what else? Oh, I took a mathematical physics course from Van Vleck.

Ashrafi:

Do you remember...?

Slichter:

Then I, and I later took an electron physics course from Purcell. I donít remember the exact order in which I took these things, but I started research that summer, the summer of Ď47. So, I entered graduate school in the fall of Ď46. And, that summer I started work with Purcell building an electron spin resonance rig. And...

Ashrafi:

So, Purcell, was there, do you know if there was much conversation between Purcell — there must have been — and Van Vleck was, about the direction of this research?

Slichter:

Well, I, you know, I really donít know. The — Purcell took a, took a course with Van Vleck when he was a graduate student, and he, together with a guy named Malcolm Hebb, did some calculations of the electric splittings of the ground state, states of various magnetic ions. And, you know, these were things that were important for heat capacity for adiabatic demagnetization. [Cell phone rings].

Ashrafi:

Whoops. Iím sorry. I left it on because I didnít know if Iíd given you my number, or knew it.

Slichter:

Thatís fine. Iíll let you just take it.

Ashrafi:

Iíll get it later. Iím sure itís not big deal.

Slichter:

Uhm, anyway, uhm, so there was some papers by him and Purcell, which Purcell wrote, and Purcell was embarrassed about. He used to say, well, he didnít really know much about those papers, didnít understand them very well, because he was — Malcolm Hebb, I guess, was a postdoc, and Purcell was a graduate student. I know, I know enough to discount what Purcell said, when he says he doesnít know something. ButÖ

Ashrafi:

So, did you propose your project to Purcell?

Slichter:

No. I went to Purcell and said that ďProfessor Van Vleck has suggested this.Ē [Beep] And, I my guess is that — look, the logic is that undoubtedly Van went to talk to Purcell, and said that ďThis would be a great — how about doing some electron spin resonance on these things?Ē And he probably said, ďI have a suggestion of someone who could do it.Ē And, I had no experience with microwaves, of course, but Purcell knew a lot because he had been in a radiation lab. And, so I, with Purcellís help, and Bob Poundsí, both had been in a radiation lab, and also George Pake, who was a year ahead of me, why I designed a microwave cavity to do these experiments. And, actually, I did a lot of sort of construction invention in it, you know. For example, I made the cavity tuneable by having a phosphor bronze disc, which put some ridges in so that it could be moved up and down with a screw on pressing against it, you know, so I could adjust it this way. I had a tuneable cavity, which was useful.

Ashrafi:

Youíve never mentioned in our conversation so far, some background that would allow you some facility with this kind of work?

Slichter:

Well, uhm...

Ashrafi:

At Woods Hole, I suppose?

Slichter:

Well yes. You know, in the summers, my grandfather, Charles Slichter, had a wonderful shop. And, he did a lot, he did a lot of sort of work around the place, his summer home. He put in his own plumbing, or heating system, hot water heating system. And, he allowed my brother and me to use any tools that were in that shop. And, we used to make sailboats, model sailboats, and stuff like this. And I, my, and also at school there, why I did a fair amount of making very simple little boat models. AndÖ

Ashrafi:

This is at high school?

Slichter:

High school. Yeah.

Ashrafi:

Or Harvard?

Slichter:

Yeah. No. No, high school, and junior high level. You could — there was some, there was a company that sold model kits for — you know, these, Iím not talking about a really fancy models. Iím talking rather simple models. But they were, but you know where you carved the balsam wood and glued things together, and stuff like that, you know. So, I liked to do that type of thing. And, I was always very much interested in wood carving. I remember, we went to, my father had a sabbatical leave in 1937 and we went to Europe for about six months. And, some of the hill towns in Italy, Perugia for example, there were, youíd go by these, go by these shops inside of which there was a wood carver, you know, doing, making carved panels and stuff like this. And, I was just totally fascinated with that. And, in fact, wood carving is, has been a hobby of mine. I havenít, you know, I have trouble keeping my hobbies going because I really, when I get spare time I tend to put it in on physics. But, Iíve, you know, Iíve carved various animals and stuff. Each of my children has an animal name. And for the four older kids, Iíve all carved them one. For example, my oldest son, Summer, who works for Senator Feingold, is the bear. So, for him Iíve carved a napkin ring which has a bear on it. And, for the others, you know, the animal.

Ashrafi:

So, you were already used to handy work, —

Slichter:

Yeah.

Ashrafi:

— before?

Slichter:

Yeah. And, at Woods Hole, of course. a lot of hands-on stuff there, building. I designed and built a set of four oscilloscopes that we used for some experiments where we needed very low, good low-frequency response on the oscilloscopes, and which we installed on the Atlantis, this oceanographic vessel, and went down to the Bahamas. This was in the, this was in the spring of 1945, where we were trying to just to study the oscillations of the gas bubble thatís produced after the explosion goes off. There was a theory that the, that the gas bubble was attracted to solid surfaces. I mean that, I remember, that was one of the theoretical papers that I remember looking and being utterly amazed that anyone could do those calculations, I mean, I couldnít understand the math in the papers. And, that, it could well be that when a depth charge damaged a submarine, it was not because of the initial explosion at a distance, but that the gas bubble was attracted to the submarine, and its second pulse was up against the submarine, and because it was a lower frequency thing might do, might be more destructive. So, we wanted to study the gas bubble oscillations, and measure the pressure time curves that you got from them. But, the problem is that if youíre in shallow water you get reflections from the bottom. And, so, itís just junk. And so thereís a place called the Tongue of the Ocean, which is very, very deep. And, so we outfitted the Atlantis to go on this trip. And, I mean this is my first big responsibility, because I had designed and built four oscilloscopes so that we could have four different channels of an oscilloscope whose response went all the way down to DC, which is hard to do, because if you get drift, you know, it drifts off scale. So, I was the electronics guy who went down there, and I built the equipment for this, and then ran it. And, so this was a, this was terrific experience.

Ashrafi:

Thatís two things you took from Woods Hole that affected your later work. Or, three things. One is an attitude towards simplicity, —

Slichter:

Yeah.

Ashrafi:

— or simplifying problems. The second was, your experience in working through the mechanics book. And, the third was the electronics experience you got?

Slichter:

And, a fourth, which is a, which was my enormous respect for physical chemists —

Ashrafi:

Right.

Slichter:

— and physical chemistry, and what those guy knew.

Ashrafi:

Okay.

Slichter:

And, not a feeling that thatís dirt, you know, or something like that. But, this, but there was terrific intellectual power in that field, among the practitioners of that field.

Ashrafi:

What was your reaction to being directed towards being an experimentalist?

Slichter:

Well, I think I probably always thought I would be an experimentalist.

Ashrafi:

Oh. Okay.

Slichter:

And, so I didnít feel I was being directed to it.

Ashrafi:

Okay.

Slichter:

And, but I, but you know the, Purcell was a terrific theorist as well as being and experimenter. And so was Bob Pound. When I started work with Purcell, why the, Bloomberg was just finishing up. He was Purcellís first student, and George Pake was, had already started work. And so, Bloomberg was around for a few months, and then he left. And then Pake was there. The basic papers that Purcell, Pound, and Torrey, and so on...

Ashrafi:

When you took your PhD qualifying exam?

Slichter:

Oh. Yeah. At Harvard, you, to get a PhD you had to, at that time, you had to present four fields. Two of the fields were normally satisfied by coursework. One of them was, then the third one would be the field of your thesis. And, then the fourth one would be a field which you would present in an oral exam. So, I picked electronics as the — electricity and magnetism electronics, basically, as the fourth field.

Ashrafi:

As the...?

Slichter:

And I had Curry Street, and Chaffee, and I forget who the third guy was on my committee. Anyway, they, at the start of the examination why they asked me, they said, ďWhat do you plan to be, an experimental physicists or a theorist?Ē So, I said, ďI want to be a physicist. I want to be, I want to do both.Ē And, they, they pursued trying to get me to say which it was. Well, I think of myself as an experimental physicist. I am an experimental physicist.

Ashrafi:

And, when did you stop saying that ďI want to be a physicist,Ē and start saying, ďIím an experimentalist?Ē

Slichter:

Oh, well I mean I just said that to them, —

Ashrafi:

Uh huh.

Slichter:

— in this exam. Thatís where people were asking me that. If people ask me what I am, Iím going to say Iím an experimental physicist.

Ashrafi:

Uhm-hmm.

Slichter:

And, but, you know, I like to try to, I like to try to understand and explain the experiments. I donít like to do experiments and have some other guy explain them.

Ashrafi:

Uhm-hmm.

Slichter:

So, but look, I know I donít have the mathematical abilities and so on to be a really powerful theorist. I mean, there are people who tell me that Iím, could be a theorist if I wanted to be, but, but I think my, my deepest talent has been to identify a significant problem, and devise and experiment to study it. You know, of course, when you devised experiments, as an experimenter youíre always working within a certain realm, because you canít, you have to have apparatus. And so, you work within a regime of things, and you may design specialized apparatus for different things, but you canít, letís say, this year be a guy who does neutron studies, you know, and the next year be an optics guy, and the year after that be a low temperature physicist, because thereís so much expense and expertise, and you have to, you know, to within an arena. And, the other thing is, if you want to be on the forefront, you have to be on the forefront in the techniques and things. And so, you, and that takes time. So, theorists can probably move around more readily than experimenters, because thereís more transfer.

Ashrafi:

More transfer?

Slichter:

Thatís possible.

Ashrafi:

You mean between topics?

Slichter:

Yeah.

Ashrafi:

Okay.

Slichter:

Yeah.

Ashrafi:

When you started research did you stop coursework?

Slichter:

No. I still had, I think I took, I probably took coursework for two years.

Ashrafi:

Okay. Did you work much with other students? Or, were you working mostly with alone?

Slichter:

No. Working alone.

Ashrafi:

Okay.

Slichter:

Okay. So, I actually, I did really two sorts of experiments for my thesis. The first set of things I did was to, I built a microwave rig using a klystron, and I studied the electron spin resonance of several different ions: iron, and manganese, and chlorine — I mean copper — in some salts.

Ashrafi:

Uhm-hmm.

Slichter:

And, this is right at the very beginning of people doing electron spin resonance. And, one of the things that I did in connection with this was to realize that people were using bridge apparatuses to — and they would balance the bridge to detect the signal, and that always gave you a signal which was the square root of the sums of the squares of the real and the imaginary part of the electron spin susceptibility.

Ashrafi:

Okay.

Slichter:

But, what you really would like to be able to do is look at the absorption spectrum.

Ashrafi:

I see. Uhm-hmm.

Slichter:

Or the dispersion.

Ashrafi:

Uhm-hmm.

Slichter:

The absorption spectrum is the imaginary part, from the imaginary part. Well, in nuclear magnetic resonance apparatus the people were, had a bridge and they would run it, adjust the bridge balance so that they could pick up the real or the imaginary part. And so, I mean so this is not a great deep insight, but I realized that I shouldnít run the bridge balanced, I should run it unbalanced, but tuned to resonance and so that I had a large reflective signal on top of which was a small electron spin resonance signal, and whose phase was picked out by the phase of the signal, which was present with it. And if I, if that signal, which was present, was the reflection from a cavity at resonance, then I was going to get the absorption signal.

Ashrafi:

Uhm-hmm.

Slichter:

So, I mean it was kind of at that level. So, so I had some innovated things to do then, and I took some of these spectra and then Purcell got the idea that it would be interesting to try to measure spin lattice relaxation times by electron spin resonance using the technique which they were using in nuclear resonance to so-called ďsaturationĒ technique, where you look at the size of the NMR signal as you run up the power level of the signal generator. And, for low powers, the signal is proportional to the driving field, but it levels off, and then falls off. And, that happens when the power going into the spin system is coming in faster than the system can get rid of, and its temperature rises to a new temperature. So, he suggested I should do that, and so actually I built a second rig. I got a magnetron to generate very high power, and did the first measurements. These are the first measurements by electron spin resonance of electron spin lattice relaxation times. So, that was the second part of my thesis. AndÖ

Ashrafi:

How was that lab organized? Did everyone work with Purcell? Was there a hierarchy? Was everyone working together?

Slichter:

No. There was Purcell and — look, when I — I mean, I was Purcellís third student.

Ashrafi:

Right.

Slichter:

And, shortly, I guess about the next year, why some other students joined the group. And, when I started out, why, there was just Pake. I mean Bloomberg had gone, and there was just Pake, and me then. And, then Pake started working some with Herb Gutowsky, whose was a chemistry graduate student who came over and — so the two of them are working together a bit. And then, Pake and Gutowsky got their degrees in Ď48, and Raymond Andrew came as a postdoc, as a Commonwealth Fund Fellow. Heís no longer living, but became a very famous guy. And, he and I were, occupied two basement labs, which were separated by a wall through which there was a giant hole that had been cut because someone had an optical path they wanted to use for some sort of detection thing. And, so we would converse every morning through that hole in the wall, and then go on about our work. But, so, so that was basically — and, you know, I rarely saw Purcell.

Ashrafi:

Oh.

Slichter:

AndÖ

Ashrafi:

So, you mostly were working alone then?

Slichter:

Yeah. Very much alone. AndÖ

Ashrafi:

So, you saw Purcell once a week? Once a month?

Slichter:

Well, I mean, I would see him come in, —

Ashrafi:

Uh huh.

Slichter:

— and when I was — the first work I did was on the, you know, up above ground, and his office was off of the one where I worked, so Iíd see him when he came in. But, basically, you know, we werenít talking about science. He was very, I mean he was quite interested in what George Pake was doing, and I was pretty much by myself. And, then he told me, he said, ďWell, you should write your stuff up.Ē So, I finished up then in June of Ď49. And, what happened was that in the, letís see, in the fall of Ď48, Wheeler Loomis, came to Cambridge. And, one day Purcell came into the lab and said, ďHave you talked to Wheeler Loomis yet?Ē And, I said, ďNo. Who is Wheeler Loomis?Ē And, he said — Now, Wheeler Loomis had been Purcellís boss at the radiation lab, because Loomis was the associate director of the radiation lab.

Ashrafi:

Okay.

Slichter:

And, I think Purcell, I think Loomis came to Harvard to see if Purcell had a student. He came to Harvard to recruit. And, Loomis was a Harvard PhD. And, anyway, he, so later on I, that day I saw him, and Loomis invited me out to the University of Illinois. And, I came out, I donít know, and that might have been in December. I think it was probably December of Ď48, to visit. And, I wasnít asked to give a seminar. I mean, I didnít have a thesis finished.

Ashrafi:

Uhm-hmm.

Slichter:

But, so it was evident that Purcell must have said Iíll probably finish up in June. And, Loomis offered me a job.

Ashrafi:

During your visit?

Slichter:

Yeah, during the visit. Well, I had heard that Frederick Seitz was going to come to Illinois, the rumor was out. And, I, George Pake, you know, had seen these, done, looked at the proton resonance of water molecules in gypsum, and had seen the spectrum where you could see that the two hydrogen atoms were near each other in the water molecule, because it split the spectrum from being a single line, in to a doublet, because the neighbor could have a spin point either up or down, and thus created an extra field, which could have either of two values. So, instead of a single line he saw a pair. And, he and Gutowsky had looked at some, then, a class of compounds, chemical compounds which had CH2 or CH3 groups in them, and they had discovered that even in a solid state you could see the molecules rotating, and things like this. So, I thought this was very interesting stuff, and I thought that, you know, condensed matter physics, you know, this was just sort of coming on the line at that time.

The transistor had just been invented, and this looked like a really hot field, and so I thought that really the thing, once you do a magnetic resonance is to use it as a tool to study problems in solid state physics. And so, I had heard this rumor that Seitz was coming here, and you know, he was really sort of Mr. Solid State Physics at that time, because of his famous book. And here it is, right here. And so, I asked Loomis if this was true. And, he said, ďWell, weíve offered him a job, but we donít yet know whether heís going to come.Ē So, I said, ďWell, can I wait [Laugh] to give you my answer?Ē And, there was one other job opportunity, Rabi was looking for someone to come to Columbia. And, I asked Purcell, ďWhich should I do?Ē And he was, you know, very, he didnít like to get into things like this, but he said, ďWell,Ē he said, ďYou know, if Rabi liked you, Columbia would probably be a good place to be, but you knowÖĒ I think basically he was, was alerting me that he, you know, youíd have to have on your mind what Rabi thought. And, I, and I just decided that the idea of being around Fred Seitz was just so terrific. And, I got a phone call from Loomis a few weeks later saying ďSeitz is coming.Ē So, I said I would come.

Ashrafi:

Did you talk to Van Vleck about these decisions?

Slichter:

I donít think so. I mean, just Purcell. But, no.

Ashrafi:

Is there anything more we should talk about in Harvard experience, before we talk about Urbana?

Slichter:

Uhm.

Ashrafi:

So, youíve got a topic — Oh, I meant to ask you, did you, so you had this. You had this program of using solid state physics, using NMR to study solid state physics?

Slichter:

No, it was going to be an ESR.

Ashrafi:

Iím sorry, ESR. And, did you discuss this larger program with anybody?

Slichter:

No. Now, I, when I came out here, I had one idea in mind, which was that there was a thing called an F-center. Are you fairly knowledgeable about solid state physics?

Ashrafi:

Not too knowledgeable. No.

Slichter:

Okay. Well, you know, in the alkali halide, if you have, thereís a center thatís created if thereís something like a chlorine. So, letís take sodium chloride, where you have sodium-plus ions, and chlorine-minus ions. If you heat this in a sodium vapor you end up with a material which has a few more sodium atoms than chlorine.

Ashrafi:

Okay.

Slichter:

So, some of the places where a chlorine atom should be are empty.

Ashrafi:

Okay.

Slichter:

But, that place should be negatively charged, so what happens is that the excess sodium gives up its electron and the electron goes into one of these locations, and that causes the crystals to have a very deep cover. Theyíre transparent otherwise, but they get deeply colored. And so those are ďfarbenzentrumĒ, or color centers.

Ashrafi:

I see.

Slichter:

And, —

Ashrafi:

Okay.

Slichter:

— that, and the, one can see them optically, if they were present, and one knew how they were formed, but the question was, ďWhat are they?Ē And, the thought was that this was an electron spin trap there. So, I thought this would be an interesting thing to try to look at with an electron spin resonance. So, when I came out hereÖ

Ashrafi:

This was a well-known problem, orÖ?

Slichter:

Yes.

Ashrafi:

Okay.

Slichter:

Yeah. This was well known.

Ashrafi:

Okay.

Slichter:

And, I mean I think people, what I would say is this, people knew that this was a trapped electron, —

Ashrafi:

Okay.

Slichter:

— but, you know, I didnít know any solid state physics. I mean, I had sat in on some lectures that Van Vleck gave, —

Ashrafi:

Okay.

Slichter:

— but I really didnít know much. And, the second thing is, electron spin resonance requires that there be an unpaired electron. Most systems donít have unpaired electrons. I mean, take sodium chloride. The sodium is a sodium-plus, which is a closed shell, and chlorine is a Cl-minus, which is a closed shell, and thereís no electron spin that isnít paired off with one going the other way. Or, take the hydrogen bond in the hydrogen molecule. An upspin and a downspin share a common orbit. So, most things donít have electron spins. And, what I had been studying was electron spin resonance. And so, I figured I should start out by trying to look at some system. And so, I was trying, thinking what system has an unpaired spin? And so, thatís this.

Ashrafi:

Okay.

Slichter:

So, thatís about the level of, you know I figured, okay weíll build an electron spin resonance apparatus, but I want to at least know something that I can look at.

Ashrafi:

Now, this thought that youíre recollecting, is thinking as you did at Harvard, or after you came to Urbana?

Slichter:

No. I think probably when I was at Harvard, I was thinking that this was what I was going to do.

Ashrafi:

Okay.

Slichter:

Now, I had in mind a way of making a much more sensitive electron spin resonance rig than previously. I was going to make a so-called superheterodyne apparatus, which I had not had before. But, I knew this would enable me to make yet more sensitive apparatus. There were really two ways that one could make a more sensitive apparatus than the one that I had. That was one way, and then the other way — and then you detect the microwave signals using crystals, crystal diodes. And the other way of doing it is, was to use bolometers, which gave very good, very low noise. And, so I, when I arrived here, there was already nuclear magnetic resonance going on. You probably know that.

Ashrafi:

Uhm-hmm. Now, who was doing it here?

Slichter:

Well, Erwin Hahn. And, I — Erwin Hahn — I should probably tell you, this is probably a good time to tell you about the starting of nuclear resonance here, —

Ashrafi:

Okay.

Slichter:

— because it ties in on this right here.

Ashrafi:

Can I ask you one question before we leave Harvard?

Slichter:

Yeah.

Ashrafi:

Do you know who funded your work at Harvard?

Slichter:

I have no idea. The, and look, we want to come back and talk about funding, —

Ashrafi:

Okay.

Slichter:

— because this, I have a very unique story to tell you there —

Ashrafi:

Okay.

Slichter:

— about my funding. Anyway, Erwin Hahn was a radar technician in the Navy during World War II, and was an undergraduate at Juniata College and he came here to Illinois, and was hired as a research assistant out on the betatron. And, at that time, Don Kerst, there was a betatron here but Don Kerst was building a big one, a 340 MeV betatron. And so, Erwin was hired, along with other graduate students, to work on the construction of this. He did that for a while and then he just realized this isnít what he wanted to do. He wanted to do a different type of thing. So, he talked to a professor named James Bartlett, who was a theorist, who at that time had an interest in biophysics, and asked him about the possibility of doing something. And Bartlett said, ďWell, you know, thereís this interesting stuff that Bloch has just done, and why donít you read those papers, and maybe thereís something you can do there.Ē So, he read the very first papers that Felix Bloch wrote about nuclear induction, nuclear magnetic resonance. And, so he decided to build an NMR apparatus. But, because of the fact that he had this background in radar and pulse things, why he thought it would be interesting to look at would be some of the transient effects that Bloch described in his paper. So, he set off to do that. And, that was his thesis. He basically was an, was, did this unsupervised. I mean, he had no help. But, he did have a, he hired an electrical engineering student as a technician, who knew a lot of electronics, and so on, and helped him build this, build the rig.

Ashrafi:

Uhm-hmm.

Slichter:

And, he actually came and visited Purcell while he and, both Hahn and I were graduate students. Wheeler Loomis, and this is so typical of Loomis. Loomis decided that Erwin should have the benefit of going to talk with Purcell, and so on. So, Loomis paid for a trip for him to come to visit Harvard, and I remember meeting him there. And then he, of course, returned, and he finished it, and we both got our degrees in June of Ď49. And, so when I came out here, why there was already nuclear magnetic resonance. Now that, I came out in September. I stayed on and worked at Harvard doing more electron spin resonance that summer, and then I came out here in September and Erwin was already, Erwin, that summer, had discovered spin echoes, which were a big discovery. Which, he discovered quite accidentally, you know, by, because he was looking at pulses and looking at the NMR signal right after a pulse, looking on the oscilloscope, and he happened to put on two pulses which were sufficiently close together that, relative to the duration of the oscilloscope sweep, that in addition to have this single right after it, this other signal popped up, which was the echo. And then, of course he was alert and he followed that through. And then, he worked out the explanation of it, using Blochís equations to describe their presence. So, that had happened. And, Dick Norberg, another student, had started to work in nuclear magnetic resonance, as well as a student named Ed McNeil. AndÖ

Ashrafi:

And theyíre working with Hahn?

Slichter:

They, well, they were really sort of working on their own, but they, they, they were kind of all in there together. They, Norberg had a technician named Kypta, helping him some, too. And, Norberg built a rig, basically copying the rig that Hahn had. So this was, they were in action when I got out here, but no one was doing electron spin resonance. There was no electron spin resonance apparatus, and I was going to have to order it, and so on. Well, about that time, I learned that Beringer and Castle, who were at Yale, and who had, I knew, a, one of these very sensitive bolometer rigs, had looked for the F-center. They had good questions of it, and they had looked for it and they couldnít find it. So, I hadnít ordered any ESR stuff yet, but that really shook me, because this was, I mean I just, I thought this was what I should do. And, just at that time, Herb Gutowsky, who was over in the chemistry department here, had seen that in, he was looking at the NMR in sodium and seeing that the sodium NMR line narrowed, which showed that in the solid there was motion, so the sodium was diffusing. But, he was very limited in how much he could study this because as soon as a line narrowed down to the width of his magnet he could no longer see any narrowing.

So, he had a short temperature range over which he could see this. Well, what I realized was the spin echo enables you to, technique, enables you to observe the natural decay time, so-called transverse decay time, which is connected with line width. In the presence of a magnet inhomogeneity is what the echo does is refocus—the inhomogeneous magnet causes spins which are precessing to get out of step. And, in the spin echo, what you do is to cause them to come back together again. So, you get rid of the magnet inhomogeneity. And, I realized that we could really study this diffusion motion in the sodium if we used spin echoes. Dick Norberg was my first student. He thought up his own thesis topic — the study of the H resonance in Pd. He used spin echoes for some of his work. This was the first paper using pulsed methods to study solid state physics. So, basically it was Norberg, using Norbergís rig, I said, ďLetís look at the spin echo in sodium.Ē So, I plunged in on that.

Ashrafi:

And that was your first project?

Slichter:

Thatís my first project. My first publication. Now, I need to tell you another thing. I never published my thesis. And, I, you know, I had these results, on the crystal splittings, and I had the spin lattice relaxation time measurements, but I didnít have out of this some really crucial thing where I could say, like George Pake had, where one had a, could develop a theory and show what this meant theoretically. And, for the spin lattice relaxation, so we had these numbers which no one else had before, but there wasnít any theory to tell the significance of the number, you know. And, so basically, I had these results, but I mean they were the first papers of this sort that had ever been done.

Slichter:

And, I should have published that. I mean, this, I had the first measurements of spin lattice relaxation times using electron spin resonance. I mean, you know, I should have had that on my record. Thatís what people should think. They should also realize that I was the first person to extract the absorption spectrum out of ESR. I mean, these were great things, you know. Well, not earth shaking, but they were, you know, that was good stuff, and I should have published it. And, I always want my students to publish what they do, and I, and Iím probably — and I realize that itís really important for them to have a sense of what theyíve accomplished. Mike Tinkham told me that when he started on his PhD thesis at MIT he came up to Harvard to study my thesis to learn electron spin resonance.

Ashrafi:

When you came here, was there a different mentor here for you? Or were you...?

Slichter:

Well, uh, Fred Seitz. Well, itís really, Fred Seitz took an interest in all of us, and he took a real interest in me. And, he — and Iíll tell you some stories about that in a moment. But, then what happened was this, I mean, first of all, so we had this, and I got this, and we published this as a letter in Physical Review. And, so this is, this is the second use of pulse NMR to study solids, this paper, to study properties of Solids, and using Norberg and Slichter. Thatís my first publication.

Ashrafi:

Yeah. Okay.

Slichter:

And, on the basis of this I got an invitation to give an invited paper at a Physical Society meeting that was going to take place, I guess, at Ohio State. And, Iím sure that was due to Fred Seitz. But, I realized that I had a position and Norberg didnít, and so I proposed him and he gave that talk eventually. Then, Overhauser arrived. And, Overhauser had, for his PhD thesis, calculated the, which his thesis advisor was Kittel. But, he did his thesis — he started working with Kittel, while Kittel was still at Bell Labs. But, he, Overhauser was a graduate student at Berkeley. Kittel suggested a problem to him, and by the time Kittel got out to Berkeley, Overhauser had finished the problem. So, he got his PhD, and he tells about going into Kittelís office to talk to him about getting a job, and Kittel said, ďWell, wait a minute,Ē and he picked up the phone and called Fred Seitz, and Fred, and then he turned and he said, ďWell, Fred Seitz offers you a position in Illinois.Ē [Laugh] So, Overhauser came here as a postdoc to work with James Koehler, who is not a resonance guy. But, I got to know Overhauser, and he had discovered, in the meanwhile, that if you saturated an electron spin resonance in a metal, and run up the power level real high, which is what I had done for my thesis, you know, for the spin lattice relaxation, that it would cause the nuclei to become strongly polarized.

So, this was a scheme for polarizing nuclei, and he told me about it. And, but no one at that time had seen a conduction electron spin resonance. So, now, when I was with Purcell, Purcell came in one day — and this is typical of Purcell, you know, I was looking at these things like iron [501 allum] sitting in a cavity made of copper, and Purcell said, ďCharlie,Ē he said, ďWhy donít we see the conduction electron resonance of the copper in the walls of the cavity?Ē And, of course, I mean, I had never thought of this. So, and I didnít know what to say. And, I said, ďWell, I donít know.Ē So, and then the next day, itís typical, and said, ďCharlie. I know why we donít see it.Ē And, he said, ďThe microwave skin depth is very thin, and the conduction electrons are moving in all directions and they come into the skin depth and thatís where the RF, the microwave can act on them, but they bounce off the walls and go back out. So, theyíre only there for a very short time. And, consequently by the uncertainty principle, that gives you a line broadening,Ē and heíd had it worked out what the line broadening would be from the velocity of the Fermi surface and the skin depth, you know, and the typical things. As I said, he immediately had a simple way to get the answer what the line breadth would be. Eventually the theory of this was worked out by Dyson, in a very complex paper, but Purcell had the answer, the essential answer, you know, on the back of an envelope. And, he said, ďThatís why we donít see it.Ē So, I knew this. And so, when Overhauser said, you know, ďWe should try to find this electron spin resonance so you can polarize the nuclei.Ē And, the first thing I realized was, you know, I remembered this conversation with Purcell. But then I realized, you know, we were looking at NMR in metals. And, the way you do that is you use a powdered sample. And, the powder particles are small compared to the skin depth. So, the RF penetrates those powders.

So, now Overhauser had calculated what the spin lattice relaxation time should be, and it then was actually quite long down to the microsecond. And so, I realized that if instead of doing electron spin resonance up in microwaves, the way everyone was doing, I used a nuclear resonance apparatus, that the, Iíd be at frequencies where youíd have penetration throughout the whole of the particle, then I wouldnít have this broadening that had wiped it out, so we ought to be able to see it. And so, this mean instead of doing it at 3000 gauss do it, you know around 10 gauss, or something like that. And, that should have been a very narrow, intense resonance. So, I said, ďOh, weíve got to look for this. [Ringing bell]. And, my student, I had a student, Don Holcomb who had joined the group at that time — and I had two new students, Don Holcomb and Tom Carver. And Don later became a professor at Cornell, and Tom at Princeton. Anyway, so we got some copper powder, and got some silver powder, and various several other metals, I donít remember, and we looked. And, we were looking for a very narrow resonance, with our nuclear resonance apparatus. And, I built a solenoid to supply the static magnetic field. It might even be somewhere in here. Iím not sure. Itís sitting around. You know, about this long. And, with a collection of coils on the end to make the field more homogeneous, and so on. And, we spent several months looking in vain for this. And, we tried our sodium sample, and didnít find it there. But, so eventually we gave up.

Ashrafi:

This is when?

Slichter:

So, this is — do you have my publication list there? [Laugh] All right. So, so this must have been Ď51. Probably. Possibly Ď52. Iím not sure. And so, so Don switched topics, thesis topics, to extend the work on alkaline metals to lithium, and he worked with Dick Norberg, who was staying on as a postdoc there. And then, one day I went down to the library and a new Physical Review had come in, and there was an article by Griswold, Kipp, and Kittel reporting the electron spin resonance in lithium metal, and they were working at microwaves. And, indeed you could see this broadening that Purcell had talked about, but it turns out there was, is a sharp component in this broad thing. And then Dyson worked out the theory of this, eventually, with a complete line shape. But, I saw this thing and I realized, my god, I mean, that it was much, much broader than the prediction of Overhauser.

It was five gauss wide, and we were working about 10 gauss and we were looking for a really sharp thing. You know, we didnít were modulating the field and so, I rushed up to the lab, and I took the lithium sample out of Holcombís rig, and I went in, and we had some little oscillators, so-called Transitron oscillators, where we would put water in the coil and use this to measure the magnetic field of our electro magnets, just measure the frequency of the proton resonance with that apparatus. So, I took the water out and put the sodium in and stuck this in this solenoid that I had, and connected it to a Variac, and there on the oscilloscope was a giant lithium ESR. So, of course, I felt awful, [Laugh] you know, that we didnít have it, didnít see it first. Letís see. Well, Iíll show you in a minute. But, anyway, Holcomb was now off on another topic, so Tom and I immediately set to work to try to first of all study this resonance, and then go to work trying to do the Overhauser, verify Overhauserís idea. And, I guess we, we probably were working on this probably starting in around January.

Ashrafi:

Of Ď52?

Slichter:

So, this must have been, letís see, the year, the year that the — this is January of Ď53.

Ashrafi:

Okay.

Slichter:

And, that spring, at the Washington meeting, I went to the Washington meeting, Overhauser presented his idea on nuclear polarization to, at that meeting, and this — incidentally, did you ever find the article I wrote for this?

Ashrafi:

I found it here. I couldnít find it in Maryland, but I found it here.

Slichter:

Okay.

Ashrafi:

At a chemistry meeting.

Slichter:

Anyway, Overhauser presented this idea, and his paper, his, the abstract of this had captured the attention of all the people like Rabi, and Purcell, and Ramsey, and Felix Bloch, and they were all there in the audience, and he gave this ten-minute paper. And, in his presentation he said that Tom Carver and I were working on this experiment. And, after the, but he had to go someplace after his talk, so there was a question period, but then he had, and then they moved on and he left. And so these people, when the session was over these people came out — I wasnít in at the session. I forget why, but they came out. I had been trying — Purcell had asked me how this thing worked, earlier that day, and I started to tell him and then we got interrupted. But, they came out and they descended on me to ask me how, what was with this thing. They all felt that it violated the second law of thermodynamics, because youíre heating one thing and it makes the other get cold.

This is what they were saying. Saturating the spins, conduction electron spin, this is sort of like making it hot. And, anyway, so they descended on me, and I started to try to explain it. But then, particularly Rabi got talking and then they just quite paying attention to me and they started talking with each other. And, eventually I just wandered off, because — and so, that, so our idea was this. We had to work at low frequency, because we had to have the penetration, you know, for the nuclei as well as the electrons. But, of course, NMR signals are very weak at low frequencies and they, and typically if you want to do NMR, you do it at as high a magnetic field as you can. In typical fields that people were working at there were, you know, seven, eight, or nine thousand gauss. And I had just, this thing that I had just seen, that electron spin resonance, that was at about ten gauss, a lot lower. So, what we did was we made a compromise. I concluded that if we worked at about fifty kilocycles for the nuclei instead of 30 megahertz.

Ashrafi:

Iím sorry.

Slichter:

No. Donít worry. ThatísÖ

Ashrafi:

You worked at, you said fifty megacycles?

Slichter:

I felt that if we worked at about fifty kilocycles, —

Ashrafi:

Kilocycles

Slichter:

— which would be, I guess, probably around thirty gauss. Iíve forgotten the exact numbers. I mean, we could find them in the papers. But, way down in the kilocycle region, at low magnetic fields, that that would put the electron spin resonance up around 60 megahertz, and the nuclear resonance around fifty kilohertz. So, this was sort of the numbers. I felt we, we probably would have trouble seeing the resonance if we didnít have the Overhauser Effect, but that if the Overhauser Effect worked we could see them. And, so we built an apparatus. Now, you understand, so we built the complete NMR rig, and we also, but now we didnít have any NMR apparatus up in the 60 megahertz region, so we built and oscillator for that, and we used the radio amateurís handbook to — you know — Tom Carver was a very skilled experimenter. When he was in high school he had built a motor-controlled, radio, radio control for a motor boat. So, he would drive the motor boat around on the lake, with him on the shore.

He was a great hands-on guy. And we, so we worked on this thing. And, we eventually succeeded in getting a, so we could see a gigantic proton signal, with a sample much bigger than our metal, at this low field. But, so then we built the coils and things for the lithium. And, we had our, the rig in a metal box so that we kept out all extraneous signals and stuff like this. And, we were in there one day. I was over on one side of the room, and Tom was at the rig. And he let out this whoop. And, this is what he saw. Itís this thing here. [Slichter shows a photo of the oscilloscope signal of the Ouerhauser effect]. And this is the, this is the lithium signal without the — well, let me put it this way. To saturate the electrons we had to turn on the electron oscillator. And, this was a vacuum tube oscillator and it had a plate voltage and a power supply for the plate, and there was a switch. So, you throw the switch, you turn on the plate voltage and the thing would oscillate and produce the saturating signal. And so, what happened was, he was sitting there looking at this, and threw the switch, and bam! that just came right up on the screen. And this little signal there is the signal of protons in the same apparatus. I guess, probably the same frequency, but a different magnetic field, with a sample which was enormous.

Ashrafi:

Thereís two signals here or one?

Slichter:

Well, this is sweeping back and forth.

Ashrafi:

I see. Okay.

Slichter:

And, so you see this line twice.

Ashrafi:

Uh huh.

Slichter:

And so, that was it.

Ashrafi:

So, you got it?

Slichter:

And we were so excited. And, we rushed the paper off. And, Purcell was over in Switzerland, and so we fired it off to him, and I got just a wonderful letter, you know. This just meant so much to me.

Ashrafi:

Because of Purcellís approval?

Slichter:

Yeah.

Ashrafi:

Oh.

Slichter:

I mean, too, just this feeling that Iíd really done something.

Ashrafi:

So, this is six years after the comment about, ďYou can write a short paper?Ē

Slichter:

Yeah.

Ashrafi:

Uhm-hmm.

Slichter:

You know, I sort of debated whether to tell you this or not. I donít really want to make a bit deal out of it. I mean, you know, my, this is more a problem with me, than him, and thatís probably not something to make much of. I donít, I just, I donít, donít circulate it around.

Ashrafi:

Well, youíll get a chance to edit this.

Slichter:

Yeah.

Ashrafi:

Itíll come out the way you like it.

Slichter:

Yeah. You bet.

Ashrafi:

But, I can certainly understand how a student looking for someone, at Harvard, someone like Purcell would take every hint, every comment, —

Slichter:

Yeah.

Ashrafi:

— and read into it.

Slichter:

And, you know, I mean, these things, there are a lot of other things that relate to how sensitive one is to things like that. So, I mean, I bring some baggage to it.

Ashrafi:

Everyone does.

Slichter:

Yeah.

Ashrafi:

Everyone does.

Slichter:

Anyway, but it was, well you can see, even today. [Laugh]

Ashrafi:

So, in the meantime, you have set up a lab?

Slichter:

Yeah.

Ashrafi:

Youíve gotten funding?

Slichter:

But I didnít — okay, so let me describe the funding. The, Illinois had a big nuclear physics contract from ONR, and this funded the building of the betatron, it funded the operation of the cyclotron, and it funded the people who were working on artificial radioactivity, Maurice and Gertrude Goldhaber were here. And, so I was just under that umbrella. I never had to ó so, Loomis had control. Loomis was the principle investigator, the department head and the principle investigator. And so, you know, when he offered me a job, why the funding came with it. But, I donít remember really talking about what the funding level was. If I wanted to buy some apparatus, so I would go to him and get permission to spend the money.

But, so in a way I didnít think of it as my money, and but I mean this just went on, and I, and I was funded this way until the late Ď50s. And, at that time, Fred Seitz came around to me and said, ďYou know, you know the ONR budget has not grown as fast as the demands on it.Ē And he said, ďYou know, youíre pretty well established now.Ē And, he said, ďIt would probably be helpful to Wheeler if you could get some funding from another agency.Ē Well, I had never applied to any agency at all. And, with Purcell, you know, we werenít aware of any — he didnít talk about agencies, or reports, or stuff. I mean, he must have had just Harvard funding for his stuff. So, I didnít know anything about this stuff. So, [Laugh] I just said, ďWell, okay. Iíll do that.Ē And, I was trying to figure out how I do this. And, I suppose about four or five days later, Fred came around again and said, ďI was just down in Washington, and I saw Don Stevens at the AEC, and told him that you were interested in getting some outside funding. And, he says heíd be glad to fund you.Ē And so, [Laugh], so I started being funded by them. And, Iíve been funded by them and the agencies ever since. And, this basically, after being funded by the AEC for about three or four years, why they told us there were a number of other people who had such grants: Ralph Simmons, and Harry Drickamer, and so on. And, they said it would simplify life a lot for them if we would combine our grants into a single one. And, this is really sort of the start of our Department of Energy Materials Research Lab here. So, it was just pulling together a group of individual grants, which were, which we had. And those grants, I mean they, basically we get funded a year at a time. At least this happened, this was the way it always used to be. And, you know, youíd write about a paragraph a year to tell what you did. So, it was fantastic funding. So, I really had a life of innocence, up to and including today.

Ashrafi:

It doesnít sound like that the constraints — there wasnít much of a push or a pull, in terms of research direction, at least on funding?

Slichter:

No.

Ashrafi:

Is that right?

Slichter:

No, Iíve always just worked on what I thought was interesting.

Ashrafi:

Hmm. And the funding just was there?

Slichter:

Was there.

Ashrafi:

Okay.

Slichter:

And, well, you know, what was terrific was, you know — now right after, the Overhauser Effect just absolutely was a huge thing, because it was so surprising to people. You know, all these leaders of the field had thought it wouldnít be true. And so, that was big. And, another thing was, people were thinking maybe this was going to be a way that people could make polarized nuclear targets. And this hasnít turned out, this hasnít turned out to be easy. Itís been possible to do it, but thatís not where its impact is. Its impact, actually, the Overhauser Effect has enormous impact in chemistry. And, because itís the way in these giant long molecules where you can tell when the thing comes back. And, two nuclei which are near to each other, when the molecule comes back, have an interaction. And so, if you try to look at the spin lattice relaxation of this nucleus, you also affect whatís happening to that nucleus, and this is basically an Overhauser Effect, which is taking place in the system, but not between an electron in the nucleus, but one nucleus with another.

Ashrafi:

So, this discovery brought you a lot of attention?

Slichter:

Absolutely, and I got, gave the first invited talk Iíd ever given at the Chicago meeting of the American Physical Society. I mean it was a giant lecture hall and it was absolutely packed, and there were people sitting in the aisles, and standing around the back. It was, I mean this was — and you see it had the, it had this feature that it was, first of all, this very unusual proposal, which people had thought couldnít be true and it was. But, the second thing was, you know, this is really the first double resonance experiment. There really, there was a pre-Bob Pound actually did one before, but I mean this was a very unusual way to do magnetic resonance, and people were looking at either a nucleus or theyíre looking at the electron, and here weíre looking at the coupling between them, and simultaneously viewing them together. And, thatís a big thing, and you know, had to be a very big thing. And, that third thing about it is, that we did nuclear resonance at this frequency and this field, which is way over from where everyone else was working.

Ashrafi:

Which was?

Slichter:

Way away — I mean everyone else is working at the 7,000 gauss, and weíre down to ten to thirty gauss. And, now that then led to the next thing, which was I was in the — well, let me back up a second and say, you know when I was a graduate student at Harvard, why C.J. Gorter came through and he taught a summer school course, which I took, and about paramagnetic relaxation. And for that course why we, he had us write term papers. And so, I wrote a term paper. And part of that term paper, I estimated how, I gave an estimate of how big the electron spin resonance signal would be. And, of course this signal strength is determined.

Ashrafi:

Okay.

Slichter:

You can calculate the area under the absorption curve if you know the static susceptibility.

Ashrafi:

Okay.

Slichter:

Theyíre related by the Kramers-Kronig relations. And so, I had made an estimate. And so, then if you can make an estimate of how wide the line is, the resonance line, that enables you to determine the peak signal intensity. So, just from knowledge of the static susceptibility I knew this. And so, I had, this was in my paper, term paper, for Gorter.

Ashrafi:

Okay.

Slichter:

So, one day, this is just about this very same timeÖ

Ashrafi:

Same time as?

Slichter:

As the Overhauser Effect.

Ashrafi:

Okay.

Slichter:

I was walking down, out in the hallway, up on the fourth floor of the physics building, and there was an office where the theorists were, just down the way, and David Pines was there. And, David came out, he was a postdoc. He had been at Princeton. He had worked on basically many body effects in metals. How do you treat the electron-electron interactions in metals? And, he stopped me. He was very excited because he had just made, figured out how to make the correction to the static susceptibility of the free electron model by including electron-electron couplings, using random phase approximation. And, he said, ďThis is really exciting.Ē He said he had estimates that the change in susceptibility was as a result of the many body effects, but he said ďThe trouble is, of course, no one can measure it, because you know if you measure a magnetic susceptibility thereís an orbital contribution, and thereís a spin contribution, and you donít know how much is which.Ē Well, I said, ďDavid, I know how to measure it. Just measure the area under the electron spin resonance and that will tell you the static susceptibility. I mean, thatís been my term paper as a graduate student.Ē And so, by then you see, we had seen the electron spin resonance in lithium and sodium. And, so I had a student, Bob Schumacher, then and we set about doing this.

But, and this was what really, where these things all come together, the — of course, to determine the susceptibility you have to make an absolute determination of the absorption. An absolute determination of absorption is really tough, because you know there are losses in the coils, and how much of the loss is from the sample, and everything of this sort. And, but because weíd been doing these things where then nuclear resonance at a strange frequency and so on, I realized that what we could do was to be use a nuclear resonance apparatus, look at the electron spin resonance in that apparatus in the low magnetic field, then crank the magnet up to 7,000 gauss, and look at the nuclear resonance of the lithium nuclei. So, now the area under the lithium nuclear resonance is given in terms of the static nuclear spin susceptibility of the lithium nuclei, and the area under the electron spin resonance curve is given in terms of this static spin susceptibility of the electrons. So, I could leave the frequency of the apparatus the same, the sample the same, the coil the same, do it all at the same frequency, and just change the magnet and compare the absorption signal of lithium nuclei with the conduction electrons. Now, the, the nuclear susceptibility of lithium is, thatís a classical thing given by Curieís Law. And, one knows every, so one knows that.

So, we got rid of all the instrumental uncertainties, and they just cancel out completely, because thatís all the same. And so this gives, gave us great precision in the ability to measure this. And so not only were, so this was Schumacherís thesis. So, we measured lithium and sodium. But this was, what was really — so first of all that was a terrific experiment. Again, because it was so unconventional. And, you know, doing electron spin resonance not in microwaves but, you know, down at just a few gauss and with a radio frequency. And, let me give you a Van Vleck story. I went to a March meeting, just after this, and Van Vleck was giving an invited talk about some magnetic susceptibility on some substance. And, he started his talk out, and he said, ďNow,Ē he said, ďIím going to talk about this. Iím not going to talk about the electron spin susceptibility of metals,Ē he said, ďwhich has just been measured recently by Slichter and Schumacher.Ē And then he talked about our experiment for a while, which wasnít the subject of his talk. But, I mean this is just so like him. He put a plug in for us, you know, in this talk. And, so he was, he was like that.

Ashrafi:

Uhm-hmm.

Slichter:

And so anyway — but the thing that this also did was make me realize is, as I pointed out to you, Iím really, Iím starting out as an ignoramus in solid state physics. So, Iím learning solid state physics by my interaction with these people who are around where Fred Seitz is. And, of course David was here, not directly because of Fred Seitz, but indirectly because Fred had recruited John Bardeen. And, David had come to be a postdoc with Bardeen. And, but it opened my eyes to the idea that the many body viewpoint of solids was a really deeply fundamental. I mean how do you really talk about, how do you really talk about electrons? The normal theory of metals treats the electrons as noninteracting, but in a box. But, theyíre strongly interacting. And, one of the known [081] things they talked about how the long range interactions give rise to plasma oscillations, and then you have a residual interaction, which is the screened interaction. And so, I just thought this was a very exciting, because this is really very fundamental. And, I realized that, by god, NMR can make a measurement, or magnetic resonance can make a measurement of this very fundamental stuff that other people canít measure. And, so then that really made me feel, boy thatís really the aspect of condensed matter physics, which is the most exciting if you can see it.

Ashrafi:

And how did that realization affect the problems that you picked and that picked or that you worked after that?

Slichter:

Well, I mean the biggest thing that it did right off the bat was to, was the, you know, I got interested in superconductivity. Bardeen was here and was working on superconductivity, and I, so I realized I should learn something about superconductivity, and I, you know, studied the various papers and things. But, I heard him give a colloquium one day in which he talked about superconductors. And, this is, you know, several years before the BCS theory, and he had this idea that something happened at the Fermi surface in the superconductor, and the fact that there was a, instead of the density states being continuous, that there was a gap in it. And, that, and he said, you know, if you have that energy gap, he was pretty sure that that would lead to a, to basically the London Equations. Let me back up a second. The London brothers had this phenomenological description of superconductivity, which, in which they, where they have a relationship between the current and the vector potential. And, Bardeen felt that if you had a gap in the spectrum that youíd be able to produce the London Equations, and that basically meant that you had an explanation of superconductivity.

Because their equations were a simplified way of describing superconductors. And, well, because we had been doing this work in alkali metals why I realized that the electrons that enabled the nuclei to become polarized were the electrons right at the Fermi surface. And therefore, in the superconducting state, if thereís an energy gap there, the nuclei relaxation time should be a lot different. And, so, I thought, ďMy god. Youíve got to measure the nuclear relaxation in the superconductor.Ē So, Iím sitting in his talk. He says this. And then of course I had been studying it, and of course where the superconductor is — I mean, this is before Type II superconductors are known. And, what a superconductor does, its most fundamental property, as Bardeen would say, was the Meisner Effect, which excludes magnetic fields. So, well my, so you canít get a magnetic field into the material. So, how am I going to do magnetic resonance? But, and of course I took this course from Gorter, where he talked about relaxation, he talked about adiabatic demagnetization, and stuff like this, you know. And, these are the sorts of things that had led Van Vleck to do the theoretical things on iron group atoms, you know, which why he was interested in my doing electron spin resonance. So, you know, I had all that in my background.

And, it suddenly hit me that I, you know, — as soon as I had this idea I quit listening to Bardeen, and Iím just sitting there, and then I realized that what we can do, we could do an experiment in which, you know, if you apply a magnetic field, which is sufficiently strong, it suppresses the superconductivity. But, what we did was to put the sample in a magnet, and a magnetic field above the critical field so that the material was normal, polarized the nuclei, and then turned the magnet off. And, you have to understand, no one was turning magnets off, these days. But, so you turned the magnet off, that would be an adiabatic demagnetization and it would make the nuclei get very cold, nuclear spins. Of course, it wouldnít affect the lattice, because until the, youíd have to have paramagnetic ions in there to cool the lattice. And, this is, letís say, just an ordinary metal, so you donít expect it to cool the metal. And, the metal is sitting there in contact with liquid helium. See? But the nuclei would get very cold. And, you leave them there. And now they will, through spin lattice relaxation they will warm toward the temperature of the lattice. And then, we could turn the magnet back on again, convert the material to the normal state where we can do NMR and look at the signal, and study how big that signal was as a function of how long the magnet was off. And, that would tell us how fast the energy exchange took place while the system was in zero field.

Ashrafi:

Okay.

Slichter:

So, at the end of the colloquium, I had this idea. I had this experiment. And, I mean I really thought this was a terrific experiment. Now, there had been some things where people had taken samples out of their magnets and let them set down on the earthís field and then do things there and put them back on. Bob Pound, working with Ed Purcell and Norman Ramsey, had done some things like this, but, but the problem is how do you, you turn this magnet off and on? Well, itís clear what you could do, you could make a solenoid, and do this. And, because we had been doing experiments down at low fields — see, the field to suppress aluminum is about 100 gauss, so I figured what weíll do letís look at aluminum. It had a relaxation time of around one second, when you get down there. So, itís got to be long enough so you can turn a magnet off and on, you know.

Ashrafi:

Uhm-hmm.

Slichter:

So, the question is to find — and so you, you can use a solenoid to get a field of a few hundred gauss, which is all thatís needed to make a normal metal, that makes the magnetic resonance, you know, at a very low frequency. But, we had been doing these things at these unconventional fields and frequencies. So, I was just mentally totally prepared for doing this experiment, which was just in an absolutely oddball regime. And, so, there, there was a very bright student, Chuck Hebel, who had said he wanted to work with me, and so Chuck was a guy who started out at the betatron, and then got in, saw what was going on in magnetic resonance and came around. So my, so I enlisted him. And, we actually, instead of using a solenoid, since he had been working with the betatron he knew about these laminated iron things that, Iím not sure what the metal was, not iron but mu metal, something like that that the betatron used to generate, you know, so they could guide the magnetic field, turning the betatron on and off at very high frequencies you would, several times a second. So, we made a, we made a magnet, Chuck did, made a magnet out of betatron laminations, and did this experiment.

Ashrafi:

Do you mean these low-field experiments require some instrumental innovations on your part?

Slichter:

Oh yeah. I mean the whole — well, put it this way, the, well first of all, I mean, you just had, no you had to build a rig which would operate down there. The principles of the rig werenít that different, —

Ashrafi:

Okay.

Slichter:

— but the principle thing was the recognition that you could do it, and the, and sort of the, and the nerve to try. [Laugh] Actually, I think, I donít know whether you remember this or not, if youíve read my article in the encyclopedia of Nuclear Magnetic Resonance. When I was a graduate student, why, and I was looking at electron spin resonance things, I noticed that if you looked at the energy levels of these iron group atoms as a function of the strength of the magnetic field, some of the energies went up and some of them went down as you changed the field. And there were actually some levels which crossed each other, which meant that theyíre, that transition from one level to the other takes place close to zero frequency. And, I got the idea, I wondered if I could detect that crossover by putting my sample in a nuclear resonance apparatus. And, I tried to do that experiment. I couldnít make it work. I later concluded that we, that we had the wrong values for the electric field gradients, so that the, so we were looking in the wrong field range. But, that, that idea of using a nuclear resonance apparatus to look at electron spin resonance actually dated from my graduate school days. And so, it popped up again in these experiments here.

Ashrafi:

Okay. At some point I want to ask you about building this department, and if you had some goal administering, an administrative role in this department?

Slichter:

No. I never have.

Ashrafi:

Never?

Slichter:

No. Iíve been on various committees, and so, but Iíve never been associate head, or anything, or held any administrative position.

Ashrafi:

Do you have a feeling of such, how such a prominent physics department came to be established at Illinois?

Slichter:

Wheeler Loomis.

Ashrafi:

Thatís what people say, but what about what Wheeler Loomis did?

Slichter:

Well, first of all, he had, he understood what it took. That is, who, he had been, you know he was a very close personal friend of Rabiís. And, he had been in New York, NYU, and seen Columbia, and Harvard, and so he understood that what you wanted to get were really great physicists. And, he wanted to get them young, and grow the thing. And, so, and the second thing is, he was a person of great integrity and judgment. He was an austere person, you know, but he was — I mean, heís a great man, you know, humanly, and totally fair, but tough minded, and great judgment. And, he knew what he was looking for. He was trying to get the sort of people Columbia was hiring and Harvard was hiring. He tried to bring Rabi out here, very early on. Didnít succeed, but he got Rabiís student, Norman Ramsey. Norman came here just before the war, and then the war broke out and Ramsey left and Loomis couldnít get him back. He got Don Kerst here, and of course Kerst invented the betatron while he was here. He had Arne Nordsick, who was a really deep theorist, here. So, he had, so he was making a collection of really great people, and then, you know, he built a department and then the war came and the department evaporated, with people going off to the war. But, he could get some of them back. He had the Goldhabers here, really great physicists. Then, then he, then he realized he should start activity in solid state physics, and he went after Seitz. And, that was key because Seitz was a close personal friend of Bardeen, and knew that Bardeen was terribly unhappy at Bell Labs because of the interaction with Shockley. And, if youíve talked with Holonyak then you know all about that. And so, that got Bardeen here. And, once he had Bardeen here, why it made it very hard for any condensed matter physicist who had his head screwed on right to leave here. And, because it was just such a great thing to be near him.

Ashrafi:

Is this a good time for a break?

Slichter:

Sure.

Ashrafi:

And then we pick up?

Slichter:

Yeah.

Ashrafi:

Itís okay?

Slichter:

Yeah. Should we go get some lunch?

Ashrafi:

Sure. [Recording paused.] So, you were saying how your interaction with Pines changed the way you look at solid state physics?

Slichter:

Yes.

Ashrafi:

And, I wonder, if you then, did you learn what you needed from him? Did you take on a project with many body theory?

Slichter:

No. No. No. I was thinking about it. What I learned from him was this, I got and developed this vision that understanding things at the fundamental level, the many body problem and its various manifestations, was really the deepest sort of issue. And, so thatís why when I heard Bardeen, I seized on, you know, I got interested in superconductivity because I could see that, you know, that was one of the really big areas of science that wasnít understood. And, Pines was postdoc with Bardeen, and he was working with Bardeen on superconductivity. So then I was excited when I had devised this experiment that I told you about. And, we got our results on that, just a matter of half a year probably before Bardeen, Cooper, Schrieffer made their theory. Cooper had already developed his theory of the Cooper Pair. And, Bardeen had talked about the energy gap. What I was expecting we would find was really based on the two fluid model that people were using, and Gorter had used, that you had a superfluid and a normal fluid of electrons, and my thinking was that only the normal electrons would be able to scatter, and therefore the nuclear relaxation process is a thing where an electron comes by a nucleus.

Their spins precess around each other and in the process exchange energy and the electron is scattered. The electron goes off with a slightly different energy. And, so I thought that in this that, as I said, that this would show up there. And, I thought that the relaxation would be slower in the superconductor. At first I thought, you know, we probably just, we would simply be measuring the amount of excitations above an energy gap, or weíd be measuring the number in this other viewpoint the number of normal electrons, that this would be a very precise determination of all of that because you had a theory about conduction electrons being scattered by nuclei from the normal theory of nuclear relaxation in metals. Well, it turned out that what we found was that instead of getting slower when you went below this transition temperature, the relaxation time got faster, got twice as fast, just a little bit below the transition temperature. Now, this is the first time anyone in my group, that we had ever done any low temperature experiment. And, the liquid, and the transition — and we picked aluminum because we needed to have a slow enough relaxation time so we could turn the magnet off and on. And, we, and of course it had a critical field that wasnít too high. So, we didnít have to turn a magnetic field off that was a terribly large one. But, the point is that the transition temperature for aluminum is around 1.17 degrees Kelvin. And, this is before helium three dilution refrigerators, and all that sort of thing. And, it was just the start of our people knew that if you used, if you had helium-3 you could cool it, you could pump it down. Helium, we had normal helium. And, of course you pump on it and around two degrees you get this superfluid behavior, and itís very hard to pump far below that.

But, so we were starting at a very low temperature to begin with. But, we got help from John Wheatley, and Dylan Mapotner about how to go about making it so we could pump it. And we were actually able to pump down to a temperature which was about .85 of a transition temperature. So, we couldnít do the low temperature regime, but we could get below 1.17 K, and we saw this relaxation time come up. And, so I went to show this, to show these results to Bardeen. And, I had the following idea. I mean, he talked about there being a gap in the density of states. And, I thought that maybe what happens is, when you open those states up, so if you think about pushing the states out so maybe they build up on the edge. And, if they build up on the edge that could make the relaxation be faster. And, I tried that out and he said, ďYes, that sounds reasonable.Ē But, I mean, you know, we didnít have any basis for this other than our result. Then, one day in January, I was walking down a hallway on the second floor in the building and he came over and he stopped me. And, I think this story may be in that article. Where, you know, he was not a very talkative person. And it seemed like we stood there for hours and finally he said to me, ďWell, I think weíve solved superconductivity.Ē

Ashrafi:

I wanted to ask you, how was he? Was he excited? Was he...?

Slichter:

Well, he was obviously excited, because he had to tell someone and he stopped me and told me. And, but yes, I mean, but I mean, you know, that wouldnít, he didnít have that sort of ďWow, weíve solved, I think weíve solved superconductivity!Ē I mean there wasnít, it was very, ďWell, I think weíve solved superconductivity.Ē And of course it was wildly exciting to hear. And then he told me a bit about it. He gave me a paper to read, which, a draft that they were preparing. And then, and he showed me the, you know, their Hamiltonian, and so on, and the wave function that they had. This is all done with annihilation and creation operators and so on. And, I mean, I knew about those things, but Iíve never used them. Well, you know, this, one of the interesting things that I felt very proud of, you know, ordinarily when you calculate nuclear relaxation while youíre in the strong magnetic field and then you know the quantization of the system in this in the strong field, but the experiments we were doing we were going down to zero field. So, the spins are in the local field of the other spins, so the Hamiltonian is the dipole-dipole Hamiltonian, and no one knows the solution of that. You donít know the Eigen values, you donít know the wave functions. But, I had figured out how to calculate the relaxation time in zero field.

Ashrafi:

You were able to showÖ?

Slichter:

Show that if I assumed that at all times the nuclear spin system had a temperature, I was able to calculate the expression for the relaxation time in terms of traces. So, you didnít have to know the eigen values. You could, and so I had been able to calculate the zero field relaxation time, and its field dependence. And, so I was really anxious to see if I couldnít apply, use their theory to calculate it. And, so, so I worked it out. And, I also, Iíve always followed this policy, that I wanted my graduate students, if theyíve taken experimental data, I didnít want it to be the person who skimmed the cream and worked out the theory and they just did the experiment. So, the way you do that is that, I didnít want to not be able to work out the theory myself, but I wanted them to work the theory out. And so, I would, have, ask them to do it too. And they would, and sometimes they needed help and sometimes not.

But so that they all, they had also done the theory. And so, so Chuck Hebel, also then went through the theory. And, now because I had worked out the low temperature thing, why we had those expressions. And, we started from there and we took the BCS Hamiltonian, and the wave functions, and so on, and applied it to this, and we worked it out. And low and behold we found, yes the relaxation time should get faster. And, we showed this to Schrieffer and Bardeen. Now, I was, I thought we might have made a mistake there. There were a couple of terms, the relaxation time is an integral, involving density of states and the square of a matrix element, but there appeared to be two terms in the matrix element then. And, I was, and you know the BCS wave function doesnít have a fixed number of particles in it. And so, I was afraid that we were getting two terms because I was screwing up somehow or other on the number of particles. So, we went to Bob Schrieffer, and he said, ďNo, this is correct,Ē etcetera. Well, it turns out that if you study ultrasonic absorption and work out the theory for that, then like NMR thatís another, low-energy scattering event for the electrons. The nuclear magnetic moments scatter the electrons. And the same way sound waves scatter the electrons. And, they are also, since the sound wave frequency is low, thereís another low-energy scattering effect.

Ashrafi:

Okay.

Slichter:

And in a one-electron theory those should involve just the square of the matrix element times the density of states factors, and the Fermi functions. And, unless thereís some drastic variation of the matrix element — I mean the matrix element, some sort of average value you pull out of the integral, you know. And so, so that would be kind of a constant. So, all one-electron processes should have the same temperature dependence.

Ashrafi:

Okay.

Slichter:

But experimentally the ultrasound drops and the NMR goes up. And, Schrieffer, Bardeen, and Cooper worked through the things and they found that for the ultrasonic absorption, why it went down, and for the NMR, why it went up. And, they were very excited because the reason that these differ is because of the pair character of or the wave function. It turns out there are two matrix elements that connect the same initial and final state, and so you add them and then square them. And, in one case they add, in the other case they subtract. When we started our experiment, I knew this experiment was going to be dealing with just the electrons where the action was, you know. But, of course, BCS theory didnít exist so I did not realize it would be such a crucial test of the central idea of the BCS theory electron pairs. And, it was only after they showed us that we realized, but this experiment gets quoted as one of the first proofs of the correctness of their pair concept. And so, you know that was just a very exciting thing.

Ashrafi:

And, this is which one?

Slichter:

Hebel-Slichter.

Ashrafi:

Nuclear Relaxation in Superconducting Aluminum.

Slichter:

Yes. And, letís see. Thatís the first one.

Ashrafi:

This is number fifteen on your list?

Slichter:

Yes. And then...

Ashrafi:

And then thereís this one.

Slichter:

And then this one.

Ashrafi:

Thatís number nineteen?

Slichter:

So. Yeah. So, this is the low, this gives all — you know Chuck finished and went off, and took us a while to get our paper finally all written up. But, that one gives in it all of the stuff like the calculation of the nuclear relaxation time of zero magnetic field, you know, the use of spin temperature, and everything.

Ashrafi:

Thatís Phys. Rev. 113, 1959?

Slichter:

Yeah.

Ashrafi:

Okay.

Slichter:

And, and neither Chuck nor I had ever used annihilation and creation operators, or anything. [Laugh] Whoops. So, you know, this experiment, this is the first time weíd ever done anything at liquid helium temperature. Itís the, you know, it involves turning the field off to zero and doing with a magnet you turn off and on.

Ashrafi:

Uhm-hmm.

Slichter:

Itís an experiment where we succeeded in working out the theory of NMR on zero field, the relaxation time of the zero field. And so, I mean, itís just got everything.

Ashrafi:

You told me in the car some things that are specific to the environment to Urbana?

Slichter:

Yeah.

Ashrafi:

You said the Loomis legacy, —

Slichter:

Yeah.

Ashrafi:

— which allows you to take risks like this?

Slichter:

Yeah.

Ashrafi:

Could you describe that again?

Slichter:

Well, I mean, as soon as I, as soon as I heard Bardeen talking there and realized that measuring the relaxation time would be studying exactly the electrons he said, so thereís — his ideas should show up there in the change in the relaxation. As soon as I heard that thing, I was just wildly excited to do this experiment. And, I never thought that I shouldnít try this experiment. Same way with the Overhauser thing. I never — I mean, I was so excited about the idea of trying to polarize nuclei by saturating electron spin, as soon as Overhauser told me that I was just really excited to do this. And I mean, as I said we went after first of all trying to find the conduction electron resonance, and then, you know, failing to get it. And then other people found it, and then plunging in again, and going down to these very low fields to try to do the experiment. I was just totally focused on how exciting I was, how excited I was about, ďOh boy. If we can do this.Ē And, I never, you know, Iím always surprised when Iím kind around other people who talk about how they worried about, you know, when they were setting up. They wanted to be sure they had something that was a sure thing so they could, you know theyíve got just so many years in which to establish things. Theyíve got to get some papers published. And, I never even thought about that. It was, this was, I was in a protected environment where, and I was around people who were exciting.

Ashrafi:

Protected how?

Slichter:

Protected in that I didnít have to go out and get the research money. I didnít have to get the contracts. I wasnít worried that I was going to be fired because thereís another guy who I was competing with for a single position. I had no personal competition with any of my colleagues. We were all there together.

Ashrafi:

And Loomis told you this?

Slichter:

Yeah.

Ashrafi:

So, could you tell that story again?

Slichter:

He said to me, he said, ďI donít believe in the up or out principle.Ē He said, ďThere is a position for you here. If you come,Ē he said, ďI donít, I canít guarantee you tenure,Ē he said, ďBut you,Ē he says, ďItís up to you toÖ ďhe said, ďMy anticipation is that you will get tenure, but you will have a lot of control over how fast you get it.Ē And, but he said, ďYouíre not in competition with another person for your position, and there is a position.Ē

Ashrafi:

And, was this, is this...?

Slichter:

This is what he said to me when he first talked with me.

Ashrafi:

So, I donít know whether this was a characteristic of Urbana, or of the time, or of Loomis?

Slichter:

Loomis.

Ashrafi:

It was Loomis?

Slichter:

Yeah.

Ashrafi:

Okay.

Slichter:

I mean other, all his, most other places have these up or out things. You know, you have higher group of assistant professors, some of whom might get promoted. And, this is why we called it ďLoomis Tenure.Ē And, it was — so, you know, that was a wonderful environment. And, the other thing was, you see, its, it was part of the same — I remember, I particularly remember — well, I mean all of the faculty were like this, but you know, I was single. I was, letís see, I was twenty-four years old, a brand new PhD, and I just felt I was so warmly welcomed by everyone. I mean, most of the other people you see were in other fields. I didnít know Seitz before I got here. I went around, after I got here — I mean, I came here on the assumption that if Seitz was here that it would work for me. But, I didnít get hold of him before I came here to find out, ďMay I interact with you?Ē

Ashrafi:

Uhm-hmm.

Slichter:

And, I wasnít part of the solid states physics group. I mean, the people that Fred Seitz talked about, and specifically brought, I was brought by Wheeler Loomis. But, I think Wheeler Loomis figured he was bringing in a nuclear physicist. And, but what he knew he was bringing in one of Purcellís students, and he was bringing in someone in this brand new field, magnetic resonance. And, he did know that I was interested in Fred Seitz. But, I went around to see Fred after I got here. Fred has done a tremendous amount for me over the years. I mean, heís put me forward this, Iím sure that heís the person who nominated me for the National Academy of Sciences, you know, all those things like that.

Ashrafi:

So, how did your interactions with Fred Seitzís group develop?

Slichter:

Well, it just developed because of people who were here among the solid state people. I mean, itís interesting. Now, Dave Lazarus was measuring diffusion. Now, so I knew that people measured diffusion. That was a significant thing. And then when I, when Herb Gutowsky showed us the line narrowing in sodium, why I immediately saw that we had an opportunity because I knew that with the spin echo we could get around the problem of the magnet inhomogeneity that limited him. And so, I thought, ďWell, this will be great.Ē Now, I didnít come to this with, with a deep interest in self-diffusion of metals. I just saw an opportunity, because I knew people were interested in diffusion. I didnít really know, completely why, but I saw we had a brand new technique for measuring diffusion. Here was Dave Lazarus doing things to measure diffusion with radioactive tracers, and putting layers on the outside of a piece of material and letting it sit for a while, and then slicing away to see what was underneath it, you know, as a function of time. And, we had a thing where I could just pop a piece of metal in the coil and by varying the temperature, measure the diffusion rate of it. So, actually, I gave my first talk at an international conference in 1954, describing these measurements in the alkaline metals. And, you know there was a lot of interest in the people there, because this was a brand new technique. Magnetic resonance was a new technique.

Ashrafi:

Where was this then?

Slichter:

This was in Bristol, England.

Ashrafi:

Did you want to say more about your interactions with Bardeen?

Slichter:

Yeah. So, so, I mean, so basically, I mean, this was one big thing. He, you know, he told us about the theory, and then, and then as I said they were quite excited. But, I am proud of the fact that we did independent calculation that demonstrated — we did the first calculations of nuclear relaxation using his theory.

Ashrafi:

So, was this, was this example the first in a line of work in which thinking about things in the many body way was influential in the experiments of selected or designed?

Slichter:

Now...

Ashrafi:

Or was this the most extreme example?

Slichter:

This is the most extreme example. I, I got interested in a thing called a Kondo Effect, in the 1970s. I...

Ashrafi:

This is after Wilsonís work on the Kondo Effect?

Slichter:

No. No. This is before it.

Ashrafi:

Okay.

Slichter:

And thereís, we did a series of papers studying various atoms present in copper. Well, letís see, first, first thing there I got, I realized that we could measure the scattering of conduction electrons off of impurity atoms. And so we did some electron spin resonance experiments doing that. And then, but then what happened was that Alan Heeger did some NMR experiments on copper containing iron and came out with some — thatís a, thatís a classic Kondo system. Kondo Effect arises in metals which have magnetic atoms in them, typically in low concentrations. And, he made some statements about what he thought was happening. And, I realized that, hit upon an idea of a type of experiment that would test what he had to say. This is an experiment in which we tried to detect the nuclear magnetic resonance from the copper atoms, which were close neighbors, to the magnetic atom. And, he had published an article in which he, in fact he even mentions those nuclei as being unobservable. And, I realized then that shouldnít be true. They should be observable. And, if we could observe them, we could map how the magnetic cloud around the magnetic atom extended out into the conduction electrons in the neighborhood. And so, we did a bunch of experiments like that. And, but I could not get theorists in our department interested in that problem. And, the, so that was a source of frustration. I really came back into things, which I would call just very much — oh, then another one was a thing which I got very much interested in was Al Overhauser concluded that there, that the alkali metals had whatís known as charge density waves in them. Have you encountered, have you talked with Overhauser?

Ashrafi:

No.

Slichter:

You should do it. He would be — I hope you will.

Ashrafi:

Okay.

Slichter:

Heís a great guy. He, you know, ordinarily you think of the metal, that the charge in the metal is absolutely uniform throughout it, except for the, you know, periodicities close to the nucleus where the electrons are pulled in. Well, he came to the conclusion that the ground state of a metal actually would be one in which the charge had a spatial variation over many lattice distances. And, he talked about two types of waves, one in which the upspin and downspin electrons had their maximum densities at the same place, and thatís charge density wave. And, the other one, in which theyíre out of phase, so where the upspins are more dense, the downspins are less dense, and thatís called a spin-density wave. And, so he thought they existed in the alkali metal. So, we made an effort to find those, and looked in potassium in particular. That was the thesis of my student, Dave Folstead. But, he, we couldnít find any signs of it. We found the resonance, and from the resonance you could tell that they werenít there. So, so Al said for many years this was the only experiment he couldnít explain.

Ashrafi:

Uhm-hmm.

Slichter:

And, he still thinks that there may be some explanation. But anyway, that was another sort of many body thing. But then, of course, I got really back in to begin with high temperature superconductors. And, but all along, why I have, you know, tried to think as much as possible in terms of these more fundamental types of questions. Now, in the early l960s, I got asked by Don Hornig, who was the presidentís Science Advisor —

Ashrafi:

Uhm-hmm.

Slichter:

— to join one of the panels of the presidentís Science Advisory Committee.

Ashrafi:

Is this with Kennedy?

Slichter:

No, this was actually, I think this time was just when Johnson had come in. And, it might have — the first part might have been under Kennedy, Iím not sure. But, there was a panel on military aircraft, and the chairman of that panel was Dick Garwin. Do you know him?

Ashrafi:

Yes.

Slichter:

Anyway, evidently he proposed to Hornig that they should invite me to be on this one. Now, I did, I said, ďLook, I donít know anything about military aircraft.Ē And, Hornig said, ďWell, the idea is the rest of the panel does, but they just wanted to have generalists to, sort of, you know, ask those kind of questions that you ask if you donít know anything about it.Ē And so, this was, and the reason I got proposed by Garwin was, you know, because he liked the Hebel-Slichter experiment. And so, you know, I think thatís how he became aware of me. So, so I did that and, for several years, and then I got, when Garwin retired from the presidentís Science Advisory Committee ó those were four-year terms ó I was asked to become a member. So, from 1965-69 I was on the presidentís Science Advisory Committee. And, I went to Washington almost two days a week for four years, on different panels.

Ashrafi:

And, was this classified work?

Slichter:

A lot of it.

Ashrafi:

Okay.

Slichter:

And, then towards the end of that time, why I was put on the Committee for the National Medal of Science, and then I was chairman of that for three years. And, that was an interesting time because as a, one of the people who proposed for the National Medal of Science was Edwin Land. And, in the, so I met him then, and then he joined the committee and was on it. And, we had a really interesting time together, because both he and I felt that in the engineering fields the person should be a person who had made a scientific contribution, not just be an engineering administrator. And, we really saw eye-to-eye on that. Anyway, Iíll come back to that in a moment. In 1970, you know, Harvard had had a lot of turmoil, and two of the members of the Harvard Corporation were retiring. You know, Harvard has these two governing bodies. One is the Harvard Corporation, and the other was the Board of Overseers.

Ashrafi:

Okay.

Slichter:

The Board of Overseers, there are thirty members, and they are elected by the alumni, and they serve for, I think, itís six-year terms. Five of them every year get elected for six-year terms. And, they also include the president and the treasurer. And the other body is the Harvard Corporation, and it consists of the president, the treasurer, and five others. And, they are basically a self-perpetuating body. They propose their own successors. And, the tradition was that people served until age seventy, and then not beyond age seventy. And, two of the people were retiring, and I got invited to be a member. Now, I hadnít had anything to do with Harvard. I hadnít done any fundraising. I hadnít been active in alumni affairs, or anything of that sort. I think probably what — I wrote, had written, you know they sent a letter around to all the alumni and I had written a letter proposing — I thought the perfect candidate for the Harvard Corporation, at that point, was George Pake, who had, you know, had been Purcellís student just ahead of me. And, he had been a professor at Washington University. And then he went out to Stanford as a successor to Willis Lamb, when Willis Lamb went over to England. And then, he had come back to Washington University where he had been the Provost. And, he was a brilliant scientist. He was — he became the head of the physics department of Washington University at age twenty-eight. So, I mean he was, he was a fantastic administrator, and a really deep scientist. And, I thought that, boy, thatís what Harvard needs. And so, I wrote a long letter about him and named all the people who knew him, a lot of people who knew him, and the things heíd done. And so, I think they were very much interested in him. And, I, but they probably had other letters. But, at that time George was really fed up with academic life, and he was just been offered a job to head of this new Palo Alto Research Center of Xerox.

Ashrafi:

Uh huh.

Slichter:

And, so he was going out to the West Coast to do that. So, what happened was they ended up evidently offering the post to me. AndÖ

Ashrafi:

What, in your experience, would people have pointed to?

Slichter:

Well, itís just that I had been on the presidentís Science Advisory Committee.

Ashrafi:

I see. So, this was shortly after that? This was in 1970s?

Slichter:

Yeah. And, letís see, I had also been — in 1961, I was the Morris Loeb Lecturer in Physics at Harvard for a semester. And, the, and when I was there I wanted to commemorate the occasion for myself. I actually stayed in Purcellís office. Purcell was on sabbatical leave. And so, I wrote a book, Principles of Magnetic Resonance, which was — after each lecture and before the next lecture I wrote up the material. And actually, so what the book consisted of what the lecture should have been, you know, because I had the benefit of the class discussion, and so on. And so, I had written that book. So, and then, you know, my dad was a very famous [Ringing bell] Harvard professor, and very well respected, because of his — you know, he was a University Professor. And, he was, he just was, especially in the business community knew him very well because he had been a very successful economic forecaster.

And, after World War II a lot of people said there was going to be a depression, but he said, ďNo, there wonít because thereís all this pent-up demand. People havenít been able to buy cars or refrigerators, etcetera, and they have savings.Ē But he was, so he, I think he was broadly respected throughout the Harvard faculty, and my guess is that they, and you know, I knew the physics department, and the physics department had given me a vote of confidence in that they invited me to be the Loeb Lecturer. And so, I guess the point was that, that given the crisis at the time, and they, you know, they were going to appoint academics for the first time to the Harvard Corporation, and they appointed two of us: John Blum, who was a history prof at Yale, who had been recommended to them evidently by Kingman Brewster. And so, I guess it was just that set of combination of things. And so, they wanted a professor, and they felt, and also there were a lot of expenditure on sciences and I think that, so having a scientist was of interest.

Ashrafi:

Was the turmoil at Harvard in 1970 different than the turmoil at most American universities?

Slichter:

No. I think it was very similar. And, and so I served on the Harvard Corporation for twenty-five years. And, you know, Harvard Corporation meets twice a month in Cambridge.

Ashrafi:

Wow.

Slichter:

And so, but not, of course, through the summer, but during the academic year. And, the, the first thing that the Corporation, with Nathan Pusey had told us when I was asked if I would become a member, that he was planning to step down, so we would have to look for a successor. I went to, you know, I had just been going to Washington a tremendous amount and I wasnít sure whether I wanted to do this. It was such a big job to go so often. And, I had been, was invited to go to New York City to meet Keith Kane, and Al Nickerson, but two of the Harvard Corporation members, one of them, Keith Kane was stepping down — so, I met the person whose place I was invited to take. And, it was just the most moving experience, because it was the character of these guys, their humanity, their integrity, their intellect. And then, I just realized these guys are very special. And, they chose me. [Laugh] But, I just realized this was a fantastic honor, you know. I mean, this was not just another job. And, because these guys, you know, this was the group that had to finally decide whether or not, when McCarthy went after Wendell Furry they should fire him. Well, anyway, so that, so I did that.

Ashrafi:

Now how did you, how did you manage juggling all of this travel with your research and your students here?

Slichter:

Well they, I was able to make a schedule for teaching courses where I would teach two one and a half hour classes a week.

Ashrafi:

Uhm-hmm.

Slichter:

And...

Ashrafi:

How about your graduate students?

Slichter:

And, well, when Iím here I was active with them.

Ashrafi:

So, was it a big change in the way that you worked, to be...?

Slichter:

Well, Iíll tell you the real problem was that I think it, you know, it made it much harder for me to really keep actively —

Ashrafi:

Uhm-hmm.

Slichter:

— thinking about all that was going on in physics. Incidentally, just about that time, in the early Ď60s, I had a, I had a wonderful postdoc, Peter Mansfield. And, this is kind of interest because he, in the early Ď70s, is one of the co-inventors of magnetic resonance imaging.

Ashrafi:

Oh.

Slichter:

And, you know, he shared the Nobel Prize, two years ago, with — the same year Tony Leggett got his Nobel Prize, why Peter Mansfield and Paul Lauterbur, from here, shared the Nobel Prize for magnetic resonance imaging.

Ashrafi:

Okay.

Slichter:

And, but anyway, I think thereís no doubt that it interfered with the intensity with which I could focus on physics. So I, I mean I think itís fair to say I probably made a professional sacrifice by doing it, and probably a family sacrifice.

Ashrafi:

Now, when were you married, the first time?

Slichter:

Well, the first time I was married was 1952. And, my wife and I got divorced in 1977.

Ashrafi:

And, you have six children?

Slichter:

I had four children by that marriage.

Ashrafi:

Okay.

Slichter:

And then I was single for a few years. And, for a while I thought my first wife and I might get remarried to each other. And then, she met someone else and decided to get married to him. And so then I started thinking about who do I know? And, I remembered Anne Fitzgerald, who I had met a few years earlier on that trip to China. And so, in 1979 when my first wife told me she was going to get married to this other guy, why I started looking around and started seeing Anne, again, and we decided to get married. We got married in 1980.

Ashrafi:

And you said, do I recall correctly, that two of your children had gone on in science?

Slichter:

No, only one.

Ashrafi:

And one in engineering? Is that right?

Slichter:

No. No. No. Daniel, who graduated from Harvard last June, as a physics major, and heís going to Berkeley next year. And, this year heís working for Juan Carlos Campuzano at the University of Illinois — Chicago. And, he did a lot of work in the labs while he was an undergraduate at Harvard. And then my son, our son, David is a sophomore, and heís a psychology major. I guess I donít call it — maybe thatís a science. I donít know.

Ashrafi:

I donít recall, so you didnít mention engineering? I was wondering.

Slichter:

The engineer is my, my motherís father —

Ashrafi:

Okay.

Slichter:

— was an engineer, —

Ashrafi:

Okay.

Slichter:

— civil engineer, railway engineering was his field. This was the — I mean, itís very interesting. If you think about it, so this was around the, just the early part of the last century when, you know, the railroads are still being built.

Ashrafi:

Uhm-hmm.

Slichter:

And so, this was his field.

Ashrafi:

And, did you want to talk about some of your students, or about your teaching in general?

Slichter:

Yeah. Well, let me say this. When I was growing up I always loved to explain things to my fellow students. I mean, I was frequently in a situation where I understood something and they didnít. And I, I really enjoyed, very much, trying to find ways for them to see what was happening. And now my grandfather, Charles Slichter, was quite famous as a teacher, and, and he, and so I always thought of this as, you know — I was very, I only, I feel very particularly connected to him I suppose, not only because I had his name but because we spent summers next door, and he was a wonderful, warm, lively person.

Ashrafi:

This was the one who had the shop?

Slichter:

Thatís right. Thereís a wonderful book about him, a biography of him, which is called, ďThe Golden VectorĒ. [Ringing bell] But, you know, when he became dean of the graduate school at Wisconsin — he had an enormous capacity for the enthusiasm for the accomplishments of other people. And so, he was kind of a mentor-type. And he had, thereís a building named after him at Wisconsin too. The Bardeen, and Van Vleck, and a Slichter buildings. [Laugh] But he, he is, was really the leading person in the founding of the Wisconsin Alumni Research Foundation, you know, which is really the first of the university things in which they took a patent. This was the steenbok patent for vitamin D irradiation. And set it up in such a manner that the university got proceeds, which then funded internal research. And, thatís a very famous thing up there.

So, so I always had this feeling, you know, about teaching and things like this, that this was — when I, but as I said Iíd never taught before I came here, except for these sorts of informal things. I did some tutoring of people as an undergraduate at Harvard. But then, about a month before I was coming here I just, Iíd wake up, ďHow can I do this?Ē I was so nervous, the idea of, ďWhy on earth did I accept a university job?Ē And, for most of the first year that I was here, why on the days when I had to teach ó I started out teaching just sections in the elementary course. On the days in which I taught I couldnít eat breakfast before, before teaching. But, once the class got started, you know, once it was, the hour was underway, I really loved it. And, I do think, if you talk to my colleagues, why I do think Iím an exceptionally good teacher. I do, I think itís, I think that I do have some of this ability that I mentioned about Purcell and Bob Cole, to take complex things and present them in very simple ways. And, itís something that Iíve always wanted to impart to my students, and I really, I like to tell my students, you know, ďThereís only me between you — Iím the only person that stands between you and Purcell.Ē [Laugh] I mean, youíre that close to Purcell.

And the, you now, this book I wrote when I was a Loeb Lecturer, is, is a very well-known book. And, there is a third edition out. If you go on Amazon.com you can read reviews of it. [Laugh] But, but itís something that, so teaching has been something which I really have enjoyed, and in particular itís, I find it exciting to try to convey to people how interesting the subject is, and to make it, make it, make them really understand it in-depth. Iíve had, I think itís sixty-three students got their PhDs with me. And, there, I mean thereís a lot of interesting people. One of them, of course you know Judy Franz. My first student, Dick Norberg, who for many years was head of the physics department at Washington University. And then I told you about Bob Mieher, who is, from the farm, who was head of the department at Purdue for a long time.

Ashrafi:

Uhm-hmm.

Slichter:

And then Tom Carver was, went to Princeton and was a professor at Princeton. And, Don Holcomb was at Cornell, and he was chairman of the department on numerous occasions there, and then president of the American Association of Physics Teachers. Judy was also. I had a student, Bill Simmons, who was the chief engineer building the Nova laser at Lawrence Lab, which was the, you know, the worldís largest laser, until recently.

Ashrafi:

Uhm-hmm.

Slichter:

And, he won a big prize for this [the Simon Ramo Prize]. You know, I, many of them became professors. Others went to places like Bell Labs. And so thatís been a big part of my life. And, I have, I just really derive a lot of pleasure from the personal interactions with the students.

Ashrafi:

How would you characterize your teaching?

Slichter:

With them, or in class?

Ashrafi:

Letís say with them, first.

Slichter:

Well, what I would say is this. I like to, first of all I like to talk with them about the physics and about what it involves.

Ashrafi:

As opposed to — what do you mean by physics?

Slichter:

I mean, why are we doing this, and what are we learning?

Ashrafi:

Uhm-hmm.

Slichter:

You know, so someone gets, comes in with an experimental result, ďNow, how do we understand it? And, what is taking place in that?Ē I, one thing I like to do is this. If thereís a, I might say, ďOh, thatís an interesting result. You know, it would be interesting to calculate the following thing.Ē And then what I like to do is suggest a calculation. And then leave them to do it.

Ashrafi:

And these are students — do the students think of themselves as experimentalists, —

Slichter:

Yes.

Ashrafi:

— when they come to you?

Slichter:

Yeah. But, one reason they come to me is because they see that there are experimentalists who do a lot of theory.

Ashrafi:

Okay.

Slichter:

And, so itís kind of the overall — I mean it makes them feel like a complete physicist. I mean, theyíll, you know to do magnetic resonance you learn a lot of bread and butter quantum mechanics. And so, one of the experiences they had, you know, they take the quantum mechanics course and then they sit in on a course on magnetic resonance that I teach and then they suddenly say, ďAh, now I really understand quantum mechanics,Ē because itís, you know, itís wonderful concrete examples which youíre using. And so, I, the other thing is, that they often comment on, you know, is to, is that thereís an atmosphere of excitement in our group, because I really get excited about a new experiment. And, when youíve got something you want to do, I mean it, I canít help it. I just really, I really want to do it. And, I, we donít work on something unless I think itís worth working on, but I donít sort of demand that it be a Nobel Prize thing. But, if thereís something I see which we can do, where itís, you know, itís just this elegant thing if you do it. But, thatís so exciting. And I, when a student makes progress on it, you know, and weíre getting these results, why I want them to feel that theyíre really doing something and that theyíve accomplished something, and you know, theyíve done something to be proud of. And, I feel it.

Ashrafi:

Have there, have there been any major dead ends?

Slichter:

Oh sure. Periodically you start on something and you have to abandon it. I mean, I told you about Don Holcomb starting trying to find the conduction electron resonance, you know. And so, you know, if, you know thereís only so much parameter space to explore when youíre not finding something. And, you always kick yourself around because you didnít explore some of the parameter space. I mean if we, if I had decided that we ought to look for a much broader resonance lines than we were looking for, we would have been the people that had discovered conduction electron spin resonance. And, you know, I really understood what we were up to in that experiment, but I didnít focus on the idea that the resonance could be so much broader than Overhauser had predicted. I should have, you know. Well, I was young, you know. Itís, I mean, but thatís — I mean, you donít have to just be young to screw up. But itís, you know, you canít always think of all the things you should.

Ashrafi:

Sure.

Slichter:

And, what was another, my student Bob Miehers, his first thesis topic for him, we had to abandon, and then he did something different. And so, weíve had to do that on several occasions.

Ashrafi:

Have you ever been involved in industrial consulting?

Slichter:

Yes. I was...

Ashrafi:

Can you tell me about that?

Slichter:

Yeah. I was the, I was a consultant — first of all I was a consultant in a patent suit with, for Texaco Development, who were involved in the — they had the first patent claim for an NMR apparatus to go down an oil well. And, the, but they had never built one, but some other companies had built them. Chevron, and so on, had built oil well logging rigs, and Texaco claimed that their, that their patent predated it, which is true. And then, but the defense of the other people was that the Texaco patent wouldnít work. So, I was involved in that lawsuit, and Texaco won.

Ashrafi:

When was that?

Slichter:

Oh, that was in the Ď70s, early Ď70s. And, actually, Schlumberger now has an oil well logging thing which is very similar in many ways to the Texaco one. But, I mean this is something where you have to decide, ďCould this be made to work?Ē And, so I went through the analysis. At first I thought, ďThis is a crazy way to do it,Ē if what Chevron had was correct. And then they said, ďBut thatís not the issue, whatís the best way. The question is can it be made to work?Ē And, then I was on the — letís see, I was on the IBM Science Advisory Committee. I was a consultant to Texas Instrument.

Ashrafi:

Now, when were you on the IBM Advisory Committee?

Slichter:

Letís see, IBM Advisory Committee from the mid Ď70s to the mid Ď80s, I guess, something like that.

Ashrafi:

Okay.

Slichter:

And, I was also on the, chairman of the Science Advisory Committee of United Technologies.

Ashrafi:

Can you tell me what these involved?

Slichter:

Well, these involved going to meetings once a month or once every other month, something like this, and having technical presentations given to us, following which we would make comments about the direction of the research, —

Ashrafi:

Uhm-hmm.

Slichter:

— and things, which might be interesting opportunities to follow up, or things which didnít look as though they were going to be rewarding.

Ashrafi:

Can you judge whether or not these meetings influenced the direction of research taken at these companies?

Slichter:

Oh. Well, I think they did. What I would say is this, you know you always ask yourself, if you go do something like that, whether youíre doing something valuable for them. And, I have a base. I consider that there is a base benefit. There may be more than this, but thereís a base benefit, which is what made me feel that it was a worthwhile thing to do. And, that is, that in preparation for one of these meetings, the people in the lab have to think about what theyíre up to, and try to put together an account of it. For a group of people coming in who in general have a reputation which makes these people want to do well and follow them. And so, the members of — these committees, all of them had other scientists who I was really happy to be with. And so, I think that they, they definitely had a major benefit for those people. Now, you donít expect that youíre going to come in and make a suggestion of a whole new direction on research, which then has revolutionized the company. Those things are, donít come about in that mode. But, you can help the people in the company who want to go in one direction by supporting what they have to say.

Ashrafi:

So, IBM, United Technologies...?

Slichter:

Texas Instruments. And then, I was on, then I told you about meeting Din Land when I was appointed to the Harvard Corporation, then we were looking for a successor for Nathan Pusey, why I was assigned to go visit with Din Land. And, I had an appointment. I expected to see him about a half an hour, but he kept me there for about two and a half hours while he talked about different people, and got on the phone and called someone in England, and stuff like this. And then, several years later he called me up and asked me if Iíd like to be on the board of directors. And so, thatís the only time Iíve ever done something like that.

Ashrafi:

Of Polaroid?

Slichter:

Of Polaroid, yeah. So, I did that for...

Ashrafi:

And, that was when?

Slichter:

Well, letís see, that started in the mid Ď70s, and went to about, I guess twenty years. That was, that was interesting. And, I really liked, you know, the technical — you know, it was a very interesting thing. The different atmosphere being at the Harvard Corporation as opposed to being at Polaroid, or the other companies. You know, the technical people are so straight forward, and itís just, people are, thereís no monkey business. Itís just very, everybodyís out in the open, and itís, and Iím very much at ease in an environment with technical people, talking about technical issues. And, but, you know, itís just, you know, was a much more of a strain at Harvard in comparison with, you know, the — these arenít, werenít technical people.

Ashrafi:

When did, when was Polaroid, did it go bankrupt?

Slichter:

Yeah. It went bankrupt several years ago. I retired from the corporation quite a while before they got into their real financial troubles.

Ashrafi:

Okay.

Slichter:

But, you know, I can see, there are two things, first of all Land was very much a believer in silver halide, and Polaroid made one technical error, which was to not spot rapidly that magnetic recording was going to be so good for movies. And, Land has invented an instant form of silver halide movie film, which, spent a lot of money doing it. And, that came out just about the same time that people came up with the magnetic tape for movies. And, of course, the magnetic tape for movies is so much less expensive. And so, that, Polaroid used a lot of its resources on that. Then the other thing is that the advent of digital photography came along, and Polaroid has some terrific research programs underway in that area. I mean, this basically was taking place after I left the board, but I know about them. And, they had some absolutely fabulous digital film that they had developed. Not, the development was not completely completed at the time that they really ran out of funds. And what happened was digital photography just came on so fast. And, of course, digital photography really is a killer for Polaroid, because you know people can see instantly on their camera screen they can see what pictures they got. Now, you donít have the picture in hand, there, but one of the big things with Polaroid was that you saw whether you got the photo.

Ashrafi:

Letís see. How about the onset of computing? Did that affect your work much?

Slichter:

Oh yeah. First of all, in the, around the late Ď70s and early Ď80s, why magnetic — computer control of NMR rigs came in, and I had a wonderful student Claies Makowka who now works for IBM, who got us first into that. And now, I mean, itís completely computer controlled, and itís really important. Secondly, just for data analysis, and for modeling, and for solving equations and things like this. We just, I mean, weíd be hopeless without computers. The other big thing that came in, of course, was superconducting magnets, because a, I mean we have in the lab now, we have an eight tesla, and a nine tesla magnet. Well, you know, one tesla was a high magnetic field when I came out here, to Illinois. We didnít have any one tesla magnets. We had a .7 tesla. And, so having these high fields just makes a tremendous difference in the sensitivity. And, of course great field stability. A magnet in the superconducting mode, it just sits like a rock. And so, this enables one to do a lot that one couldnít. But, the computer control enables one to do pulse sequences, which really revolutionized things.

Ashrafi:

Can you explain?

Slichter:

Well, in these, hereís an illustration. If you — a very nice invention, which was made by my student Dick Norberg and his student Irving Lowe, uses whatís called magic angle spinning. And, magic angle spinning, you take your sample, and itís spun about an axis that makes whatís called the magic angle. Thatís the angle for which three cosine squared theta minus one is equal to zero. And, where theta is the angle between the spinning and the external field. Very often, if you have a solid sample, and youíre looking at carbon resonance, or something like this, that resonance, you might have a powder, and that resonance would be very broad. And, it has several different lines in it, which have different chemical shifts corresponding to different positions in carbons in a molecule. Youíd like to know what those chemical shifts are.

If you put the sample in a spinner, and you spin it at that magic angle, it causes those things to average to zero. But, when they, and so, when they average to zero, then what you have is the chemical shift youíve have if the thing, if the molecule was in a liquid. And then you would get sharp lines, and each chemical position would have its own individual sharp line. So, this is very useful for structural determinations with molecules. Now, at the same time, George Pake discovered if you have two protons near each other it splits the resonance into two, and from the spacing apart of those lines you can tell how far apart the nuclei are. This is the dipolar coupling goes one over R cubed. And, so when you spin you lose that sort of information. But, people have now invented ways whereby when they are spinning the sample, they observe the resonance with pulses in which they time the pulses in synchronism with the spinning speed. And, if you do this, it turns out to be possible to recover some of this dipolar splitting so you, so you get back some of the things which you want, which spinning removes, while at the same time having the benefit of splitting. And, but to do such a thing as that, you really want to be able to set up pulses and control when they occur, and how strong they are. And, so being able to just program a computer to having it controlling your apparatus just — there are many other examples, but this is just, just one where there are things you couldnít do very successfully without this.

Ashrafi:

So, computer control of experiments, data analysis, and modeling of experiments are things you use computers for?

Slichter:

Right.

Ashrafi:

And this begins in the late Ď70s and early Ď80s?

Slichter:

Yes.

Ashrafi:

And when do you start using superconducting magnets?

Slichter:

Oh, probably around 1970?

Ashrafi:

1970?

Slichter:

Yeah.

Ashrafi:

And, were there other major changes in your techniques or apparatus?

Slichter:

Well, there were, yeah. I mean, look, the very first experiments that were done with pulse NMR — well, first of all, the original NMR that people did was steady state, where you just have an oscillator running, and then maybe you modulate the strength of your magnet, so that you move off and on the resonance, you collect the signal which is synchronous with that. And then you have the discovery of the use introduction of pulse techniques, and the spin echo by Erwin Hahn. We immediately got into that business, here. Erwin left after a year, went out to Stanford as a postdoc. But, we immediately got into that to measure...

Slichter:

In the steady state things, people did signal averaging to improve signal to noise. But, with the pulse technique one, in order to be able to do that sort of thing we introduced here, Dick Norberg and Don Holcomb, introduced the use of whatís called a boxcar circuit, which basically is a gated volt meter that turns on at the time of the echo, records the signal, and takes that signal and uses it to charge a capacitor through an RC circuit. So, you have a charging time constant, and that defines the bandwidth. So, you could do signal averaging with that. But, that method did not, was good as long as the signal was bigger than the noise. But, once the signal got smaller than the noise, why that no longer, for technical reasons I donít to go into, no longer worked. But then, then we introduced here, I introduced, with my student for this thesis of my student John Spokas, whatís called phase coherent detection of this. So, that, then that was, that came into magnetic resonance, and thatís what really enables one to do signal averaging and pulse experiments and enormously improve signal to noise. And, then Norberg and his student Irving Lowe pointed out, discovered, that if you apply a ninety degree pulse and record the signal after that — thatís called free induction decay — and take the Fourier transform of that, that gives you the absorption spectrum. So, the Fourier transform of the free induction decay is the absorption spectrum. So, instead of recording the absorption spectrum, you could record this. That idea was introduced in the late Ď50s, but there werenít much, there werenít computers available for people, and you didnít have fast Fourier transform algorithm.

Then, in the mid Ď60s, why the discovery was made by Richard Ernst and Wes Anderson that if you tried to take high resolution spectra of a chemical molecule, where you have many, many lines, because each spectrum corresponds to a different position in a molecule, Wes Anderson, they pointed out that if you do a sweep through that most of the time youíre between lines. And, but if what you did was apply a ninety-degree pulse, collect the signal, and take the Fourier transform, this would enormously improve the speed at which you gather data. And so, that was introduced. And so, all, suddenly all the chemists, in stead of doing steady state experiments switched in the mid Ď60s to doing pulses. And, of course, the physicists had been doing pulse NMR since 1949.

Ashrafi:

Uhm-hmm.

Slichter:

But, the chemists got into it then. And then, then, but then you had very complicated molecules. You had all kinds of lines. Well I should say, then, in the Ď50s, Herb Gutowsky here, in chemistry, discovered that the position of the NMR line, letís say of protons, was quite characteristic of what sort of part of a molecule it was in. So, the proton line of a proton and a CH2 group was at a characteristic frequency which was different of that of a proton and a CH3 group. And, in fact, it even depended upon what things were attached to it. And so, that opened up the possibility of NMR for determining the structure of molecules. And, another discovery here, which was made here, was that if, letís say, take the molecule PF3, the phosphorus nucleus and the fluorine does, but the, and in the liquid those lines are narrow because the dipole, dipole coupling vanishes. But, if you look at the phosphorous line you see itís actually split into four lines by the three spin halves of the fluorines. And, thatís called J-coupling. And, J-coupling, we discovered that here, and independently Erwin Hahn discovered it the same time out at Stanford. And, this, together with the chemical shift, are the real bases for the determination of molecular structures.

But then, in the Ď70s, Jeener pointed out that you could make, apply pulses in a certain manner and collect your data, and make whatís called a two-dimensional NMR, where you, the pulse sequence, the pulses have two times in them, a time one, and a second time two that follows that. And, you collect data as a function of T1 and as a function of T2, and then you do a Fourier transform of T1 and T2, and now youíve got a two-dimensional Fourier transform. And, from the Fourier transform you can tell which lines correspond to the coupling and which chemical shift nucleus, to which other chemical shift. And, it enabled one to make much more, to determine much more, the structureís much more complicated spectra. This is, this is the thing for which Richard Ernst got the Nobel Prize, was exploiting this. Itís interesting.

He shared the Nobel Prize for doing — and he got the Nobel Prize for doing two things. One of them Fourier transform NMR, and the other this double-resonance technique. The Fourier transform technique was invented by Norberg and Lowe, and the two-dimensional NMR, invented by Jeener. But, Ernst really saw the significance, how to use them to determine structure if complex molecules did the exploitation of it, and saw its, power of both of these things and brought them into high-resolution NMR. So, there have been these developments of understanding of how to do NMR. And then, of course, you had the invention of imaging, which had been taking place continuously over the history of NMR. And, it has continued to be like that. And, continues to this day to have such inventions taking place.

Ashrafi:

Were you, did you ever consider moving elsewhere?

Slichter:

Well, I had a lot of chances. [Laugh]

Ashrafi:

I can imagine.

Slichter:

I was, I, went and visited other places: Columbia; MIT, twice; Harvard; Cornell, twice; University of Chicago, twice; University of Wisconsin, twice, Carnegie, Tech, UCSD, Brown, Rochester, U of North Carolina. [Laugh] But I, but I, you know, at Wisconsin I was offered the Charles Slichter professorship, named after my grandfather. [Laugh] But, you know, I really, I just felt that, that my situation here, from the point of view of science, with the colleagues and so on, was too good to leave. And, I was, you know this is especially while Bardeen was alive, just having — because the people who were around him — but I mean, Dave Pines had around him — now in recent years with the high temperature superconductivity, Dave Pines was very active here, and he had these wonderful postdocs. I had lots of interaction with these sorts of people, and, and we have wonderful facilities here, with the Materials Research Lab. My support was so simple. I just — you know I hear people talking about all of the — Iíve never had to been supported by NSF. NSF is a terrible place to have your support. The support is so little.

They, you have to keep coming back in and getting evaluated from scratch. So, you donít have any sense of stability. And, I just, itís, gosh that makes a difference. You know, so this place has such a set of things that made life in science here so easy, and so, you know, with such good colleagues. I just, every time I looked at it, I just said to myself, ďYou know there are lots of interesting places, and interesting departments.Ē Gosh, I remember when George Pake went out to start the Palo Alto Research Center, he invited me to come out and join him. And, I remember I went out there, and there I was in Palo Alto, looking at this beautiful countryside and everything, and I said to him, I said, ďWhy canít I live in a place that looks like this?Ē But then I realized, you know, I didnít want to be an industrial scientist. I wanted to have students. And, I really, I really work very well with students because what I love is with the students, and your postdocs, this, you know, youíre thinking about something. Theyíre thinking about something. If one of you gets an idea you just run down the hall and try it out. You know, I told you about my frustration with the Kondo Effect. I couldnít get any of the theorists around here interested in talking about it, and so on. And, if you, if someone isnít working on something and you want to talk to them about it, you go in and the first thing you have to do is sort of bring them up to, talk about what the whole area is and then you tell them about your, what youíre doing, and then what it is youíre worrying about or donít understand. By then, an hour and a half has gone by and they want to do something else.

Itís totally different with your students, and with your postdocs, because theyíre thinking about it, and youíre thinking about it, and youíre, both of you are prepared for what the other one is going to say, or any questions. And, thatís just a — and I have had occasions where other people in the, other faculty members in the department were working on something, like Dave Pinesí interest in recent years in high TC, you know, or Bardeen, earlier, or Pines early, Overhauser — where they really were interested in the same problem you were, and then you have a terrific interaction. But, your students are always there. And, so you, so one gets much better ideas if you talk with someone. I get ideas talking to my students even if they have suggested an idea. Itís just the process of talking with them which makes me think of things I wouldnít have thought of otherwise, which I realize is directly a result that Iím talking with them. So, they influence you in countless ways.

Ashrafi:

And, did I understand you correctly, you really have not been involved in the administration of the department?

Slichter:

Thatís right.

Ashrafi:

Is there anything else we should talk about?

Slichter:

I donít think so. And, one of the reasons I liked the Harvard Corporation thing, or the Science Advisory Committees was it enabled me to have a little touch of whatís, of the issues of administration without having to take it on.

Ashrafi:

I see.

Slichter:

No. I think Iíve probably talked much too long.

Ashrafi:

Not at all. Thank you very much for taking all this time.

Slichter:

Well, youíre welcome.