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Courtesy of Zachary Fisk, credit unknown.
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Interview of Zachary Fisk by David Zierler on April 17, 2020,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/44382
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In this interview, AIP Oral Historian David Zierler interviews Zachary Fisk, Professor Emeritus in the Department of Physics and Astronomy, University of California, Irvine. Fisk recounts his early exposure to physics from his father, who worked as physicist at Bell Labs. Fisk discusses his interest in chemical bonding as an undergraduate at Harvard, and his admiration for professors Purcell and Ramsey. He describes his decision to leave Harvard and take a job at Los Alamos, where he attended colloquia from visitors including Rabi and Bethe. Fisk discusses his reapplication and graduation from Harvard, and his decision to begin graduate work at UC San Diego where he studied the Kondo effect and rare earth impurities. Following graduate school, Fisk describes his experiences as a postdoc at Imperial College in London, his assistant professorship at the University of Chicago, and his long-term joint appointments at UC San Diego and Los Alamos, where he worked on heavy-fermion superconductors and growing crystals from molten metal fluxes. Fisk describes his motivations for joining the Magnet Lab group at Florida State University, and then his later work back in California at UC Davis and then UC Irvine. At the end of the interview, Fisk describes his ongoing fascination with superconductivity and why his early interests in chemical compounds has remained a constant throughout his career.
Okay. This is David Zierler, oral historian for the American Institute of Physics. It is April 17, 2020. It is my great pleasure to be here virtually with Professor Zach Fisk. Professor Fisk, thank you so much for being with me today.
Okay. So let’s start right at the beginning. Tell us about your birthplace and your early childhood.
Okay. I was born in New York City, but that was just because my father had a certain paranoia about hospitals. We lived in Madison, New Jersey. I was born right at the beginning of the Second World War. I ended up being born in New York City rather than Madison, New Jersey.
Your father didn't trust the hospitals in Madison?
Well, his mother died in childbirth with his younger brother, so he had a certain—how do you say?—skepticism.
Mm-hmm [yes], and Madison was probably fairly rural at that point, right?
Well, it was on a railroad called the Delaware, Lackawanna & Western, and my father commuted into New York to work from there.
What was his work?
He was a physicist. He was working at Bell Laboratories on West Street, and during the war, or at least part of the war, he had a magnetron group at Bell Labs that he ran. He also spent a year or so in Naples during the war when they were trying to figure out how far the Germans were getting along in their atomic bomb project. My understanding was most people that knew what kinds of questions you should be asking were working at Los Alamos and places like that, and so there were a few people like him around who weren't working at Los Alamos that knew the questions to ask.
It’s a pretty unique thing to have a parent who’s also a physicist. I don't come across that that often, so I want to ask a little more. What was your father’s education? Where did he go to school?
He went to MIT, and then after that he was a Junior Fellow at Harvard, in the early days of that project there. Then he came to Bell Labs at the end of the ’30s, maybe 1939, I guess, when Bell Labs was still in New York.
When you were growing up, did he bring physics home with him? Were you exposed to physics as a kid? Did he talk about his work?
Not really, no. After the war, my father became a professor at Harvard, and we lived in Massachusetts for a while. Then he worked for Lewis Strauss at the Atomic Energy Commission for a little bit. He was Director of Research there at the time when they were trying to figure out what to do with Los Alamos and other places. Then he came back to Harvard, but eventually in 1949 we moved back to New Jersey and he went back to Bell Labs at that time.
Okay. So what years were you in Cambridge (or in Boston)?
Well, we lived in Concord. My mother’s family came from Concord, so we lived out in Concord. So that was ’46 to ’49, something like that.
But with a little interval in there in Virginia.
Mm-hmm [yes]. Now in high school, were you demonstrating an aptitude for math and science already?
Yeah. I was really interested in chemistry. When we moved back to New Jersey in 1949, I inherited from some friends of my parents a really elaborate chemistry set, and I set up a laboratory in the basement of the house. I was trying to teach myself chemistry. Then for high school I went to a boarding school and they had a pretty good science program. So I kept on with chemistry. I was always going to be a chemist - high school physics is pretty boring stuff. But when I got to college, I started out with organic chemistry in and I didn't like it.
So physics in high school was boring because you weren't challenged by it?
Physics in high school was dealing with Newton’s laws kind of things, and what was interesting to me was atomic physics. We didn't get much of that, so all my extraneous reading concerned that. Then what I found out when I got to college and took organic chemistry from Louis Fieser and physical chemistry from Kistiakowsky was that both courses didn't appeal to me. You know, organic chemistry, you memorized how the reactions worked. There was no real understanding at that time, I guess—this is the late ’50s, ’59 when I took that—of exactly how these chemical reactions worked, or at least certainly Fieser never taught us that. This was a course that had 200 premeds who if they didn't get an A in the course weren't going to go to Harvard Medical School. But I wasn’t going to go to Harvard Medical School no matter what. I was the 201th guy who wasn’t interested in that. At any rate, I switched to physics. I liked that, and I liked mathematics. I really enjoyed mathematics. We had pretty good mathematics in high school. You had a couple years of calculus and so on, and the science was good, too.
So how did it occur to you to switch to physics, given that you were bored by physics in high school? Did you realize that it was a little different at Harvard?
Well, it was much more mathematical and I liked that, and I thought that the part of chemistry that I liked was really physics.
Now you said you were interested in atomic physics. I wonder. The Cold War, did that play a role in your interest—the sort of nuclear weapons race and the Cuban Missile Crisis and things like that, or was that too far out of your orbit?
I had no interest in atomic energy or nuclear physics, per se. I was interested in how chemical bonding worked. I found that chemistry has a very personal appeal in terms of crystals. They’re fun. At some point I got into growing crystals. I liked that a lot. When you're a kid fooling around with chemistry, what you discover is you can't get all the chemicals you want.They don't let you have them.
So you start learning about how you might get these, meaning how do people make the chemicals they want? I had that kind of interest early on when I was a kid.
Now at the physics department at Harvard, who were some of the standout faculty members that you really remember?
Oh. Well, the two most fantastic ones were Purcell, who taught both a fairly general lower level course, but then he taught introduction to quantum mechanics, which was a beautiful course. Then the other really exceptional teacher was Norman Ramsey, and Ramsey taught… Well, he taught a more advanced mechanics course. He was a beautiful teacher. He was really wonderful. Those were the two really exceptional physics teachers I had.
Were there qualities that they shared that made those classes so memorable to you in terms of their teaching style?
Well, let’s see. Ramsey was an extremely upbeat guy and he was just fun and a pleasant person around with an incredible enthusiasm for physics. I remember a some student in the class asking about the stability of rotations of a tennis racket about various axes that he’d noticed because he played tennis. Ramsey gets right off on that and just has a wonderful time. It’s the kind of problem he liked to think about.
Purcell was somebody that was very comfortable in life, he just enjoyed it. I remember going into his office once and asking him about a problem, and learning that his Harvard co-op number was 1836, a number associated with the mass of the electron. H also mentioned that he had wanted to use the fine-structure constant for some other account he had but not enough number of significant figures were known at the time. That was just sort of the way he was. [Chuckling]
Mm-hmm [yes], mm-hmm [yes]. Did you have a senior thesis?
No senior thesis. And you're graduating—let’s see. You graduated in 1964, and is the plan you were going to go straight into physics graduate programs, or were you thinking about taking some time off?
In 1961 I left college and I eventually ended up getting a job at Los Alamos. I went out to New Mexico and worked as a chemical technician doing uranium assays and things like that. When I was out there, I met Bernd Matthias, who would spend summers at Los Alamos. I met him out there and he was just in the process of moving to La Jolla to UCSD. La Jolla was just starting up.
It started up 1960 or something like that. He asked me if I’d like to go out and work for him as a technician and help him set up his lab. So in the fall of 19…
Yeah, in the fall of 1961 I moved to La Jolla when they were just starting UCSD.
So this would have been what, your sophomore year?
Yeah. I dropped out when I was a sophomore.
So you didn't do a leave of absence. You fully dropped out.
Wow! What did your--
I ended up in California and then I decided, “Well, I’ll reapply to Harvard.” They took me back and then in 1964 when I graduated, I went down and became a graduate student with Matthias in La Jolla.
Mm-hmm [yes], mm-hmm [yes]. So what were your impressions of Los Alamos when you got there? What was it like?
Well, they’re very isolated. It was a very isolated town, you know. It was quite a bit smaller than it is now. It was a government town.
The government owned everything. I got there in the summer of ’61, and in the summer a lot of the old-timer Manhattan Project people would come back and visit such as Hans Bethe and I. I. Rabi. We had colloquia from these guys, and it was really wonderful to see these old-timers. The man who became Theoretical Division leader after Bethe went to Cornell after the end of the Second World War was Carson Mark. I was quite good friends with one of the Marks’ sons, Tom Mark. I spent a lot of time at the Marks’ house, and I saw a lot of these old Manhattan Project people there. It was a wonderful experience getting to know some of these unusual scientists.
Los Alamos at that time still had very much an intellectual vigor that was left over from the incredible intellectual power that was there during the Second World War. It actually survived. Just jumping ahead, some of that survived into the late 1980s. In the background there were people who were really intellectually interesting, guys like Stan Ulam, who had been quite a good friend of my father’s. People like that were just fascinating. The other thing about New Mexico that I liked was that the prehistory out there is very interesting. It’s a fascinating place just to walk around in the backcountry. Still is.
So you're a 19-year-old kid, 20-year-old kid in Harvard. What’s the connection to Los Alamos? Is it through your father?
Although probably it was not his intention for you to drop out of school, I imagine.
No, I don't think so. [Laughter] Hardly. Yeah, hardly.
Did you make a promise to yourself or to him that you would reenroll at some point, or you were really thinking about not going back?
I’ve never been a person that had long-term plans. My high school, the prep school I went to was pretty intense, and actually when I got to college, in a certain sense, some of the courses I initially took I didn't find I was getting that much out of them. Probably my problem.
Now when you got to Los Alamos, were you working on sensitive stuff? Did you get a clearance?
Yeah, I had a clearance. Well, everybody that worked there had a clearance. You didn't work there without a clearance.
Right, right. And so what kind of stuff were you working on? Did you have the sense that it was like national security type stuff?
No. I worked in an analytical chemistry group. They’d send in pots of solution that contained U-235 and you’d analyze how much it had in it because, of course, how much 235 you can have in a given place—you know, you don't want more than a certain amount and so on.
So it was just working with radioactive stuff.
Mm-hmm [yes]. How was safety? What were safety protocols like at Los Alamos, working with this stuff?
The building I worked in was a very large building. When you entered the building, you walked through counters. You dressed in a locker room with protective gear, lab coat and booties on your feet. To come out back into the changing room, you had to go through counters and had to check your hands and your feet, and all this protective clothing was tossed into a bin that was washed. So there was always fresh stuff. The building, in fact, had no insulation because they turned the entire air supply of the building over every six minutes year-round, and it was all blown out through the roof through HEPA filters.
When you work there, you get regularly tested. If you're working with radioactive material you get tested regularly. You go to a medical facility and they count you. [Chuckles]
Yeah, and obviously you turned out okay. [Chuckles]
Well, so far so good. Yeah.
So you reenrolled back at Harvard; they take you back. And then are you applying to other graduate programs, or it’s because of this connection that you were all in on University of California San Diego?
Yeah. I wanted to go back, so I just went there.
Mm-hmm [yes]. What was the department like at that point? It was really up and coming?
UCSD was apparently the original idea that Roger Revelle, who ran Scripps at the time, and others had. And it was only going to be a graduate school. But that idea disappeared rather fast. But originally they got a lot of very senior faculty members there.
So it started with a chemistry department, a physics department, and a biology department. The physics department right off the bat was sort of on the map. You had Walter Kohn there, Harry Suhl, George Feher, Matthias, and Marshall Rosenbluth. There was just a whole bunch of really top people. I remember Walter Kohn remarking at some point when I was starting graduate school, that in condensed matter physics, UCSD was one of the top five schools in the country.
And it had just started.
Another thing that’s interesting about a university when it’s starting—and I saw a similar thing in a certain sense when I went to the Magnet Lab in Florida at a certain point—that initially the kind of baggage that people develop, interpersonal baggage at universities, it’s not there. So there’s a kind of wonderful aspect. Yeah.
The other thing that was interesting, especially at that time, was that it was in the Sputnik era, and so there was a lot of funding that was showing up. There was money at UCSD for visitors from all over the place. It was almost like opening your textbook, you pick a name out, and there’s the guy walking across the plaza. La Jolla where UCSD is, is a vacation spot and that also attracted visitors to UCSD.
I remember when I was at Los Alamos before, when I was working there in 1961, ’62, Rabi came out and gave a director’s colloquium in the summer, and it was entitled “What Have the Russians Done for Us Lately?” What they had done for us was Sputnik.
[Laughs] Yeah, right!
And all the research and innovation and funding that that spurred.
Yeah, that’s right, and so--
So I mean, besides La Jolla being just a nice place to live, what was it that drew all of these luminaries to this out-of-the-box program from all of the places they were coming from? Was it really the opportunity for them to have a lot of funding for new labs? Was that the big draw?
I don't know exactly how to answer that, but I think the idea that there were going to be a lot of interesting people there was attractive. I think the idea of working in a place that you would normally go to for vacation has an appeal.
And I think originally it appealed to a lot of people that it was only going to be a graduate school.
On top of that Roger Revelle was a very charismatic individual, and he managed to convince a lot of people that it was going to be fun.
Of course, there’s another guy I forgot to mention who was important in the beginning, was Keith Bruckner. The other thing about UCSD was that it was going to be the plasma physics capital. They worked out joint positions between General Dynamic and UCSD, and a group of plasma physicists that came were half at General Dynamics and half at UCSD. It turned out that General Dynamics went through a financial crisis right around then, so that aspect of it all changed. But that’s why, for instance, Marshall Rosenbluth, who was known as the pope of plasma physics was there in the beginning.
Right, right. So how did you go about choosing a mentor and a dissertation topic?
Well, I knew Matthias, and he was a wonderful screwball, a really interesting person.
Yeah. What kind of projects was Matthias working on himself in those days?
Matthias came from Zurich and ETH. He got his PhD there with Paul Scherrer and then went to MIT. Shockley hired Matthias to Bell Labs because there was a big interest in ferroelectrics and Matthias was well-known for, ferroelectrics, and the ferroelectric of most interest in those days particularly was barium titanate. A lot of the original research on it had been done at ETH in Zurich. Shockley wanted to pick his brains and so he hired Matthias. Then when he found out all he could, everything about barium titanate that Matthias knew, then he tried to fire him, which was kind of Shockley’s style.
[Laughs] Mm-hmm [yes].
But it turned out that that didn't work because Peter Debye was a consultant at Bell Labs, and Debye was what you might call the scientific grandfather of Matthias through Paul Scherrer. So Debye said, “I’m not coming back to Bell Labs if you fire Matthias.”
[Laughing] That did it.
Yeah. Well, I remember telling that story to Phil Anderson, and Phil Anderson said, “Oh, yeah. Shockley tried to fire me, too.”
[Laughs] It’s just what he does!
So how did you go about developing your dissertation topic?
Matthias’s main thing became looking for new superconductors, and particularly trying to push the superconducting transition temperature higher. His was the Edisonian approach where you just looked everywhere.
What was he trying to accomplish? What was the end goal of all of this research?
Higher TC. If you got TC high enough, maybe it could be commercially useful. That was the idea.
Mm-hmm [yes], mm-hmm [yes]. How close did he get to that?
Not very close. In Matthias’s lifetime he got to 21°, something like that. The rate at which maximum TC was going up when Matthias died wasn’t going to beat global warming. Room temperature was going up faster than TC was. Put it that way.
But he’d worked on looking at borides. There were always curious side effects that showed up with Matthias, and one of those things was he looked at the addition of magnetic impurities into superconductors to see how it affected TC, and it was generally known that it affected it strongly. Magnetic impurities affected the superconducting transition strongly, large depression, but he did a systematic study going across the rare earth series of elements starting with the first rare earth element, which is lanthanum which is a superconductor. So he put a little bit of each of the other rare earths in the series into lanthanum, and it was very systematic the way Tc changed. It actually was responsible for leading to a deep understanding of what kind of coupling causes the magnetic ordering temperatures in rare earth elements. This is something that DeGennes picked up on. But then Matthias said, “Well, how does that work with compounds? We see how it works with elements; how does it work with compounds?” So I did a study in these types of borides of that kind, but in a compound.
It’s interesting, just to give you an idea of how Matthias worked. He was really an unusual guy. Why had nobody done this systematic study before of rare earth impurities in lanthanum? Of course, it turns out that separating the lanthanide elements is difficult—they’re chemically very similar, which makes them a wonderful system. Working with rare earth compounds is wonderful because you can systematically do things because of the chemical similarities going across the series, and what changes are these inner f electrons which carry magnetism.
Good, clean rare earth elements were being produced at Ames in Iowa, you know, at the Ames Laboratory. But they were a little—I don't know what you say—a little stingy in giving them out. So Matthias invited Karl Gschneidner from Ames to Bell to give a talk. This was at the end of the ’50s. Matthias is taking Gschneidner out to dinner after he’s given his talk. Matthias’s wife, Joan, is coming along and she says, “Well, who is this we’re going to dinner with? Who is this person?” He said, “Oh, he’s the guy that’s sitting on all the rare earths.” So when Joan Matthias meets Karl Gschneidner—she had a wonderful innocence—she says, “Oh, you're the one that’s sitting on all the rare earths!” She had no idea what that meant, but it embarrassed Karl and he said, “Oh no, no!” So that’s how Bernd got all the decent rare earths he wanted.
So I did a study of rare earths impurities in yttrium hexaboride, a 6 K superconductor. It behaved just similarly to what had been seen in the case of the element lanthanum.
Which tells you what?
Well, it just says that there’s this very systematic way that superconductivity gets depressed. There was a lot of interest at that time and funding for understanding magnetism and magnetic materials more generally by looking at impurity problems. Then what happened at that time was that there was an anomaly in the series. One of the elements was anomalous, and it was cerium. This cerium had a much bigger depression than it should have had, and that was true in what Matthias had found, and it turned out to be true in this compound. Then it turned out to be also true in another compound that was being studied by another one of Matthias’s students who was there at the same time, Brian Maple. This turned out to be due to what’s become known as the Kondo effect. Kondo’s paper was 1963, I think, sometime like that, and this pushed me off into the direction of ultimately looking at Kondo effects and what are known as dense Kondo compounds. It turns out this Kondo effect survived into pure cerium compounds, for example, which was something we ran across at the time. It’s rather crazy working in hexaborides, the whole set of compounds, there’s a lot of interesting things in there, very simple kind of crystal structure. I’m still working on hexaborides, although I worked on a couple of other things along the way.
So your whole career, this is still compelling to you.
Well, there’s so much that turns up. They’re simple compounds and you can make them in very high perfection. I’ve always been drawn to materials that make well, you know, rather than materials don't make well, where you have lots of defects or other things, vacancies and other stuff like that. If interesting stuff is happening in the material, when you have a lot of disorder or defects or what have you, it gets even more complicated because life in interesting materials around defects becomes crazy.
Mm-hmm [yes]. So you graduate in 1969. I wanted to ask. You're on a college campus in the late 1960s. Are like campus protests and civil rights and anti-war movements, is this happening at UC San Diego or not really?
Yeah, the Vietnam War was a real mess.
Were you involved in any of that stuff, or you didn't get involved in the political stuff?
Not really, but there was a lot of it going on, a lot. It was very, very grim time, actually.
Yeah, yeah. Were there any women? How diverse was UC San Diego at that point? Were there minorities or women represented at all?
Well, let’s see. One of the professors there was Herbert Marcuse in philosophy. They had a philosophy department, and one of his students was very famous, or became famous, Angela Davis. But there were not a lot of women in the physics department at that time as students. There were women physicists on the faculty. Margaret Burbidge was on the faculty and also Maria Mayer. Of course, the story is always told of the local La Jolla newspaper. When Maria Mayer won the Nobel Prize, the local paper headline was “La Jolla Housewife Wins Nobel Prize”. [Laughter]
Yeah. But at any rate, there was a lot of anti-war activity, protest around there, and you could see a lot freight trains going up the coast at night with all this military type stuff on it. And March Air Force Base, you’d drive up past that, up north from here, and it was just all B-52s, just filled with B-52s and they all disappeared.
They were just all gone. So you were well aware of this, San Diego is a military town, you know? Yeah.
Right. So you defend and then you get a post-doc at Imperial College in London.
Yeah. Actually, what I got was an assistant professorship at the University of Chicago, but this person I worked with when I’d originally come out with Matthias to La Jolla in 1961 was a physicist from Imperial College called Bryan Coles. I did a superconductivity project with him—my first physics publication, actually. He said, “Why don't you come over to London and do a post-doc?” So I put off going to Chicago, but only did a year in London because the people in Chicago thought, having accepted their job, I should come sooner rather than later. So I went out there.
Mm-hmm [yes], mm-hmm [yes]. Was that a good experience in London?
It was okay. I mean it was interesting to be in London. Actually, in that group at Imperial College, there were some good people. David Sherrington was in that group .But it turned out not to be that productive a period for me. Yeah.
Mm-hmm [yes]. Now the assistant professorship at Chicago, this was tenure-track?
But you were only there for one year.
Yeah. I didn't like it.
Why didn't it work out? What happened?
Well, there were aspects of my personal life that were not going too well, and to tell you the truth, I’d never really lived in a city. Well, London was a city, but I didn't like living in Chicago in particular, although the University of Chicago is really a good university. One of the things that really interested me in going there—and really the reason I got the job—was this famous crystallographer, Willie Zachariasen, who was a very good friend of Matthias’s and who I knew because he spent winters in La Jolla. He’s the one that really set it up for me to go there, and he ended up retiring just when I went to Chicago. He was a person who had interests very much in my direction. He disappeared from the scene.
[Laughs] But then you go right back to San Diego right from Chicago.
Now you're a research physicist. Is that not a tenure-track line? What is that, research physicist?
No. You could be a research physicist, but it didn't have any tenure track. So it’s a soft money position.
Mm-hmm [yes]. Where was the funding coming from?
Well, it was in connection with Matthias—I did at one point have some of my own money from ONR, I think it was. I was working on superconducting materials. So I stayed there, actually up until Matthias died in 1980. The year before, the summer before Matthias died, I was invited to spend the summer out at Los Alamos, so I went back out to Los Alamos and worked in a group out there that Matthias had some association with. It was actually a plutonium metallurgy group. It was a marvelously diverse group. The person I really interacted with there was Jim Smith. We had some quite interesting research topics we worked on that summer, and then when Matthias died that fall, they offered me a job at Los Alamos because one of the people that was in this particular group at Los Alamos was a man that became eventually the director of Los Alamos, Sig Hecker. I’d gotten to know Sig Hecker out there, and he was a real metallurgist. He was an expert in what’s called biaxial testing, which is a particular way of testing materials. It’s actually related to how you make aluminum beer cans. It’s punching. How do you punch a can out of a disk? He was moving up very rapidly in the laboratory hierarchy, and he thought that it would be interesting to actually introduce some deeper knowledge of f electron physics into the weapons program. So in some sense, that’s the reason I got hired out there, because I was working essentially in f electron physics. The actinide elements, plutonium is one of them, are f-elements as are the rare earths. Plutonium is one of the most complicated elements crystallographically. It’s got a huge number of different crystallographic modifications, and it’s very complicated metallurgically. I don't know if you know anything about plutonium.
Of the various crystal structures that plutonium forms in, there’s a high temperature form which is called plutonium, and it’s face-centered cubic, which is a very simple crystal structure. But you say, “Okay, that’s the one simple structure it has,” and that’s the one that you can actually machine. But it’s a high-temperature structure, and just to show its strangeness, it has a negative coefficient of thermal expansion over its entire range of existence, for example, which is unusual, right? But the f electrons are very much involved in the chemistry and physics of this stuff, and so as I said, that was some part or maybe the main reason I was hired out there.
What is it like physically to work with plutonium? I mean, how does it arrive to you? How do you work with it?
To just put things in context, I worked with plutonium, but not a lot. It turned out, for various reasons, things went in some other parallel direction out there. The common isotope is plutonium-239. It’s very radioactive and it’s believed to be quite toxic, meaning that it’s chemically not good for you. To work with plutonium, almost all of it is done in glove boxes. You're extremely careful when you deal with it. In these glove boxes, the plutonium is reactive, meaning that it oxidizes, and it also tends to destroy stuff that’s in the glove boxes; namely, if you have stainless steel tools, they get bombarded by alpha particles and they slowly rust. Keeping a glove box clean to work in difficult. Everything is messy. Put it that way.
What was the end goal for the research in plutonium? What was supposed to be accomplished with this?
What was hoped was that maybe one could understand the strange mechanical and other properties of plutonium by studying various compounds—you know, that you could make compounds with plutonium. You could study them to see if they have interesting magnetic properties for example, to try to get a handle on how the f electrons are influencing the physical properties. It wasn’t highly focused. It was a very general kind of approach.
Now as a staff scientist at Los Alamos, how well connected are you with the larger academic community? Are you attending conferences? Are you reading papers, or are you sort of like in your own world there?
Yeah. Well, when I went out to Los Alamos, Los Alamos sort of had, how should I say it, not a good reputation in the academic world, to a considerable extent because it was a weapons lab, you know.
Mm-hmm [yes]. But that’s a political opinion. That doesn't say anything about the quality of the research or the people who were there.
No, that’s right. It didn't, but that’s something that you lived with. You know, there were people like Walter Kohn that were outspoken. In those days in the early ’80s, the University of California essentially ran Los Alamos, right?
But Walter and other people thought that that was a bad thing for the University to be doing, so there was a lot of hostility towards Los Alamos. The other thing I felt about aspects of working on actinide element compounds was that although there are many interesting aspects to these actinides where you could see very definite parallels to what was happening in the rare earth series, which is the 4f series—the actinides are the 5f series—that there’s always this business of if you can't work on it, people don't have as much interest in it if they can't work on it themselves, right?
So it’s a more limited community. At that time, a lot of the research being done on actinide compounds was being done at Argonne. They had very strong groups there. But you’d often go to meetings where people would present that stuff and the audience you’d see in the room would just be, “Oh, they’re Argonne scientists listening to their people,” because it was kind of removed, as you say.
You know, the actinide compounds you can work on that are essentially only mildly reactive are the uranium compounds because U-238 actually has a very long half-life. It can be worked on quite safely if one’s careful outside of places like Los Alamos. But plutonium and other materials like that, you really have to be careful with that stuff.
Now starting in 1991, you arrange to have a joint appointment between San Diego and Los Alamos. You're sort of going back and forth?
Yeah. Well, I was married. I had a new wife and we had a child. My wife was a professor at UCSD. So I had a commuting marriage.
This became sort of a joke. It turns out to have medical benefits from Los Alamos, you had to be more than half-time. It turns out that the academic year is nine months, so I had a 5/9 appointment at San Diego, so that’s more than half-time, and I had a 7/12 appointment at Los Alamos. [Laughter]
Yeah. And you would have thought… I mean in some sense it was both University of California. I was plugged into the same retirement system in both places. It was actually very fruitful because it was kind of refreshing to go between the different places, their different ideas. I got a lot from going between both places.
Yeah, yeah. And you also skipped the whole tenure process. You came on as a full professor at San Diego.
That’s right. Yeah. I recommend that.
Yeah, sure! [Laughs] That’s the way to do it!
Well, we’d had these rather spectacular successes with these uranium, heavy-fermion superconductors. I had a great deal of freedom when I went to Los Alamos. There was the general idea which I mentioned to you of what kind of use I might be to the laboratory.
But then I had this enormous amount of freedom, and I got interested in working out growing single crystals from molten metal fluxes just to see what I could do to prepare interesting things. Also, along the way I worked out kind of techniques, sort of just trivial technique for separating crystals from molten fluxes with actually using quartz wool. I used a centrifuge and could spin the melts when they’re still liquid through these things, and suddenly all this stuff was just showing up out of these melts, whereas before it was always leaching.
I’d begun doing this when I went back to UCSD from Chicago. I went to Bell Labs for a summer and worked on an isotope effect in a superconductor, ZrB12, because zirconium has a whole bunch of isotopes. It took a summer to do that job. But while I was there, I worked with a man at Bell Labs called Paul Schmidt who had a neat little induction heating rig where we learned to grow hexaboride single crystals out of molten aluminum, and that got me going on molten metal fluxes.
Also, it turned out I became very good friends with this crystal growth genius called Joe Remeika, who had been a technician that had worked for Matthias. But Remeika was really exceptional. He was one of those just natural scientists. He was totally self-educated, but he was just—what do you say?—the real thing. I learned a lot from him about crystal growth.
So any rate, I’m at Los Alamos and the big thing that had happened in superconductivity right when Matthias died was that the first heavy-fermion superconductor had shown up—CeCu2Si2—that Frank Steglich showed was actually a bulk superconductor. Many people had seen it had superconductivity, but all believed it was due to some trace impurities. But it was unique. Nobody found any other superconductors like that.
My friend, Hans Ott in Zurich who I had worked with earlier on a hexaboride. He’d taken a bus across the US one summer with his wife. He visits La Jolla. He was an extremely good experimentalist, very smart guy, and he took some hexaboride crystals that I’d grown that summer at Bell Labs back with him to Zurich to do measurements on. Then when Steglich’s result came out, Ott remembered that there’d been a really strange superconductor that had been discovered by Ernst Bucher at Bell Labs called uranium beryllium 13. Bucher convinced himself that in UBe13, a filamentary second phase was the superconductor. It wasn’t bulk, and Hans wondered whether it was a bulk superconductor or not. One of the things about beryllium is that it’s very a dangerous chemical to work with because it has this associated berylliosis, so you need to be very careful when you work with beryllium. But of course I was working at Los Alamos, and you can usually figure out how to work on anything there.
They actually had some beryllia crucibles I think left over from the Manhattan Project in the wing I was in, and I thought, “Well, gee…” So I got a hold of them and he said, “Can you grow single crystals in that? Nobody’s going to believe anything unless you can grow single crystals.”
What does that mean, you have to grow a single crystal for anybody to believe you? What does that mean?
You want to be sure there’s not some trace second phase in there that’s causing this superconductivity, and so I set out to try to grow UBe13. This was right when I was just having all this fun growing crystals here, there, and everywhere. I kept trying to grow UBe13 and was convinced that it ought to grow out of aluminum. You know, I’d look at phase diagrams, but I just wasn’t getting anything.
I’m walking down the hall one night in this building that I worked in, the large CMR building. There were all these old-time chemists around and we’d chat sometimes. There was this old guy, Clayton Olsen standing on the side there. I’d go by and he asked me what I’m working on and I said, “Well, you know, I’m working with beryllia crucibles and I’m trying to grow stuff using these crucibles.” Olsen looked at me and he says, “Oh! Yeah, those beryllia crucibles, boy, those things are just like sponges. Boy, do they soak up the water!” I had no idea that that was true, you know. Nobody I’d ever known had ever used beryllia crucibles, and I thought, “Well, maybe that’s the problem here,” I mean, even though in Los Alamos where the humidity is nothing, you know.
So I went and I baked out one of these guys and I decided I’m going to try this one more time. So I baked the crucible out before using it and then I used it. I went in and did the cool-down, and I’m leaching the aluminum out of this crucible after going through a temperature cycle but I’m not seeing anything showing up in the crucible. It was just like before; I got nothing. Then just as I’m thinking everything’s gone, I look in the bottom of the crucible and there was one crystal covering the whole bottom of the crucible. The thing must have been close to an inch in diameter. It was just this huge, half-faceted crystal that was there. Apparently the whole secret at the time was just outgassing the crucible. It turned out ultimately you didn't have to use beryllia crucibles, but I didn't know that at the time. Any rate, that got us going on this UBe13 which turned out to be very much a superconductor in the same class as this heavy fermion that Frank Steglich had discovered. Then I found another one in uranium platinum 3. This was in the middle 1980s before high-TC. It was brand new stuff in superconductivity.
So that’s what allowed me to just go in and become a professor without…
How much were you publishing? Were you really getting the word out on this research and its significance?
Yeah. We had a very extensive collaborative network, and so we were publishing a lot. I think there was one year I had 60 papers published.
I published a lot of papers.
And what was…I mean if you could just look at it holistically, what was the sum total of this research? What was the contribution of what you were doing?
Well, I mean the deal with heavy-fermion superconductivity is it’s a kind of marriage between magnetism and superconductivity because the electronic properties incorporate the magnetic degrees of freedom. There’s an entanglement between the spin degrees of freedom and the conduction electron degrees of freedom. It was a new kind of quantum material, and so it opened up all kinds of research into essentially new superconducting ground states. This was non-simple s-wave superconductivity. In a way you might have regarded it as a warm-up for high-TC and thinking about the physics and that this was a real example of superconductors which had a different kind of order parameter than the normal BCS superconductors.
What would be some of the practical applications that this research promised? What would it change?
I don't think that directly from that superconductivity there were going to be commercially useful superconductors of any kind. In terms of understanding the more general physics of superconductivity, that was important.
But you were never going to make transmission lines or magnets out of these particular guys, whereas some of the high-TC materials and so on, there was very much that hope that they could be commercialized. I think, you know, these days where superconductivity has gone is that there may be real importance in terms of quantum computing from some of these things.
So this was what you might call sort of baby steps along the way towards a deeper understanding of the general phenomena in superconductivity.
And you're answering now obviously with the benefit of hindsight, but at the time, in the late ’80s, early ’90s, could you see where this was headed? Is that sort of borne out or no?
No. You could not.
So at the time you were really proud of the theoretical contributions that you were making.
Yeah. Well, it turned out that these heavy-fermion superconductors, so-called, originally there were very few of them, but then the crazy thing that turns out is they turned out to be the one class of superconductors where we roughly know where they all are. For general superconductors you don't know where they are.
But where they are is actually at this intersect between magnetism and non-magnetism, what they call quantum critical systems where you’ve driven a magnetic transition down to close to zero and superconductivity shows up. More generally you can take that idea and see how it plays out in general frameworks for many superconductors, that superconductivity seems to be a kind of phenomenon that shows up in situations where there’s this very keen competition between different low temperature phases.
Now when you're transitioning, when you're going back and forth from Los Alamos to UCSD, are you taking on traditional professorial roles while you're on campus?
Are you taking on grad students? Are you teaching classes?
So you did take on graduate students in San Diego.
Yeah, and actually it turned out that even at Los Alamos, when high-TC showed up, we actually had a number of students that came there. There was a bunch from UCLA that came and actually more or less did their thesis topics with us in Los Alamos. George Grüner had a bunch of very good graduate students that essentially did all their thesis work at Los Alamos.
It became complicated for me, the non-scientific part was that my wife and I had a daughter, and she was half-time in school in San Diego or in La Jolla and half-time in school in Los Alamos. It turns out, as we figured out, that if you're a half-time school student in two different places, it’s very hard on a child.
Yeah. Sure. Sure.
So in the mid-1990s when they were starting up the Magnet Lab at Florida State, that was a chance for both of us to go back there. I didn't know what down south was like, and I thought it might be interesting to go spend some time there, and it was. It was interesting. It was a lot of fun.
So besides the family situation, what else was attractive to you about going to Florida State? Was the Magnet Lab just starting up?
Yep, it was quite exciting. In a certain sense, it was like UCSD in the early days, although you're going in to an established physics department, but they brought in all these other people. Bob Schrieffer went there. For me, the real attraction ultimately was Lev Gor’kov. We became quite good friends.
What was he working on at that point?
Well, he always worked on superconductivity, but he was a very interesting guy in general, but also just a brilliant physicist. He had an office next to mine and we spent a lot of time chatting.
And the Magnet Lab was an opportunity for you to continue on the same track of research, or this was a new path for you?
No, same track. Yeah.
What could you do there at the Magnet Lab that was exciting for you? What were the possibilities there?
I just continued what I had been doing before, but my family situation was much simpler.
And there’s a certain fun in going to a new place.
Yeah. I mean, north Florida was one of your strange places. [Laughter]
Did you take graduate students with you to Florida?
No. I got a whole new set of graduate students when I went there. Yeah, I’d had a couple of students from UCSD that were essentially finished, and then I just got new students in Florida.
What was the funding source for the Magnet Lab? Where was the money coming from?
Mm-hmm [yes]. Mm-hmm [yes]. What were some of the big research questions that the Magnet Lab was designed to answer?
The big success of the Bitter Magnet Lab at MIT had to do with quantum Hall type physics, I think, and there was the general hope that there was more out there of that kind.
More out there, meaning what?
Well, these were new quantum states and so that there were maybe there was a lot more to be found out and so on. That was the general idea.
How well did that play out?
Well, I don't think there’s anything that’s been as spectacular-- There’s nothing that’s been as spectacular as how the quantum Hall effect played out, but the quality of what they accomplished in terms of the quality of the magnetic fields and being able to do research, really good research, in high magnetic fields and the instrumentation and the magnets are just way better than what was there before. I mean they’ve done a really good job, I think, with what they’ve done there.
And then what were the circumstances that led you back to California, this time coming to Davis and then Irvine?
My wife died from a brain tumor, and so I started to think about how I wanted to continue. I got remarried to a woman that was a professor again at UCSD, and so I looked around to see if I could find a job in California and so I got a job in Davis. Then for various reasons, we moved back south. Well, it worked out.
And Irvine is a bigger department than Davis.
It might be. I’m not sure that’s true. They may be comparable in size. Well, they had a connection with Livermore so that there were some faculty members that were connected to Livermore Laboratory. I was quite happy in a way. At Davis, I had good graduate students there and I liked it, but it was just better for my wife and I in general to move back to Southern California, so we did.
Mm-hmm [yes]. Now in 2010 you become involved with two international efforts. The first one is in Japan. How did that come about and what was the research there?
There’s something called Japanese Atomic Energy Association (JAEA), and they have a research unit in Tokai. Tokai is a small town on the coast. It’s maybe halfway between Tokyo and Sendai. They work on f electron compounds there. You know, the total amount of plutonium they have there is like 1 gram. But they had a very nice, very competent research group there. The research unit was called the ASRC, which stands for the Advanced Scientific Research Center, and it was headed by somebody that I knew called Hiroshi Yasuoka , who had been a professor at the University of Tokyo. But when he retired, in Japan when you're 65 you retire, he’d gone and run this. There was an NMR group and an associated materials group.
They had directors for these smaller groups in there, and he asked me if I was interested in doing that. I said, “Well, I’m not going to move to Japan to do it, but I can try to oversee the group and spend a certain amount of time there each year.” So I did that for five years with that group. It was a very good bunch of people, actually. Excellent group. Really good materials people.
Are there any cultural differences in Japan in terms of their approach to doing physics?
They had a very similar approach to the way I’d done things, and in the materials group, they were actually using the techniques that we developed in Los Alamos to grow single crystals. Matthias almost never worked with single crystals, and these days that’s almost all people work with. You know, you almost don't work with polycrystals and intermetallic compounds anymore if you can…unless there’s no way you can get around it. The Japanese are really hard-working people. And they’re fun to work with. So for me that was interesting. It was a new experience to me to deal with a research group like that. I mean I’d had a Japanese post-doc, and at Los Alamos, people I worked with, there had been quite a few Japanese post-docs in our group at Los Alamos. Joe Thompson in particular had a lot of Japanese post-docs. So I’d known a lot of them. In my area of work, the approach is very similar.
Mm-hmm [yes]. In 2010, you also had an ongoing affiliation with the Max Planck Institute.
That’s right. Steglich went from Darmstadt and started this chemical physics institute in Dresden around, let me think, it may have been in early 2000, something like that. I can't remember exactly when it started, but it turned out I got on the advisory board for it, and in some sense, just by nobody else wanted to do it, I headed for several years that advisory group. Then at some point they went to the trouble to make me an external member, which is sort of like getting tenure, actually, for those things. You don't just do it. They have to approve you.
Yeah. So I’m still associated with them.
What do you like about the association with Max Planck Institute?
Well, there’s a number of people that I’ve worked with, that I continue to work with, so it’s on going research projects that I do with them. I know quite well some physics directors there There are four directors, and one of the chemistry directors and I work on a project together. I also work on some STM-type physics problems on hexaborides, actually.
There you go! It keeps coming back.
Yeah. Yeah, I just can't get away from it.
And in 2014 you become a research professor. So is that emeritus or it’s not emeritus?
Yeah. So I retired at that time, but why do I become a research professor? I still had some funding money, and so it allows me to be on PhD committees and do other things like that.
But you don't have any teaching duties.
Right, right. So Zach, I want to ask you now. I mean we’ve reached the conclusion of the narrative portion of the interview. I want to ask you a few sort of broader questions, a little more introspective about your career as a whole. The first is you’ve been recognized with numerous honors and awards over the course of your career, and I wonder if any particularly stand out as the proudest moment for you, the award that meant the most in any particular order.
Well, I guess the first award I got, which the New Materials Prize.
And this was the one from APS in 1990 you're referring to?
Yeah, and that was for all that heavy fermion work. That was a high point. Well, the second thing, which was a total surprise to me, was to be elected into the National Academy. Of course, I suppose one shouldn't say this. That’s what gave me more mobility professionally than anything. That’s the reason I was able to go from one academic place to another after that.
Yeah, or that’s what I believe.
What is it about the National Academy that does that? What do you think?
Well, in a certain sense, universities like to have people that are in the National Academy. I think that’s a fact. I don't know, but just the fact that I could go from Florida back through several University of California positions, what do you say?
What do you see? If you look at the entirety of your career, what do you see as your primary contributions to your field?
Well, I’m not sure everybody would agree with this, but what I would call almost high school simplicity of working out these flux growth techniques allowed easy access to single crystals. We discovered new materials that way and made physical measurements cleaner, easier to do.
When you say high school simplicity, what do you mean by that?
High school students can do it.
Oh, I see. [Laughs] It just so happened that you were the one to actually do it.
Well, it’s not that nobody had done that kind of stuff. The chemistry of it is very simple, but the separation technique, when I worked out this idea of how to really separate this stuff mechanically, it just suddenly becomes simple. You know, there’s often this problem, you're trying to separate crystals from a flux when it’s solid. You do it chemically—you often lose your crystals at the same time you eat the flux, you know?
So this just makes it easy. It’s easy to do. You can't do everything. You can't grow all the crystals that way, maybe not even most of them. But doing zone refining or using optical furnace methods and things like that, they’re much more elaborate to do. They require expensive equipment. This does not require expensive equipment. I could set this up in my garage, you know, pretty much. I mean you need a Bunsen burner or a torch and some other stuff, but nevertheless, it’s really simple to do. So it just makes good materials, certain kinds of materials of high quality easily accessible, and that’s a lot to be said for that.
On the scale from theory to applied, where do you see most of your work falling in terms of its contributions?
Oh, more on the theory side. Yeah.
More on the theory side.
Yeah. There’s very little of what I’ve done has had practical applications.
Has that ever been a motivating factor for you, to think about the applicability of your work? Or you’ve always been motivated by advancing the theory?
I’ve always been motivated by advancing the theory, understanding the craziness of chemical compounds, how the atomic structure affects the properties, putting atoms together, guessing how this atom might substitute into that structure in an ordered way and produce some kind of interesting property. That, for me, is one of the most fun things I’ve done.
So on that note, as a result of your work, what is understood today that wasn’t understood when you started in this business?
Well, it’s that we now know in some general way where to find these heavy-fermion superconductors, that was an unusual thing. I was not the person that first realized this. There were things I was involved with that were connected with that; I was not the one that made that connection really clear. But I also think that there’s a way you can generalize that observation that applies to a wide class, much broader classes of superconductors, but that’s my opinion—I think not a general opinion.
[Chuckles] Well, I think for my final question I want to ask you something that’s more forward-looking. You know, you're still active in your field. You're still engaged with the research. What are you excited about in the future about where your field is headed? What might be the sort of new frontiers of discovery? What are the things that are exciting to you about what the future holds?
One of the things I saw when I was a graduate student was Matthias chasing after these superconductors, and I said to myself, “I’m never going down that rat hole,” and then I discover a long time later that I did go down that rat hole. But one of the astonishing things that’s happened in superconductivity is this near or at room temperature superconductivity that these high pressure people have found in these hydrogen-rich compounds. That’s amazing that you have this phenomenon close to room temperature.
What is amazing about that?
The idea that you could get to room temperature with a superconductor seemed so unlikely. People who work in the field don't like to say this, but superconductivity always seemed like an epiphenomenon.
Room temperature is starting to be a reasonable energy, but bonding energies in chemistry are way, way above room temperature. So the idea that these in some sense low energy quantum features can survive up to these high temperatures is pretty fantastic.
The thing to say about superconductivity, though, is that somehow it’s always turned out how to be interesting. It just continues to surprise. There may be ways that one’s going to be able to get superconducting properties close to room temperature or at room temperature in certain specialized geometries like interfaces. But you're not going to make transmission lines out of things that need a megabar of pressure. It isn't going to happen, but it’s interesting that one gets there with these materials under these extreme conditions. But you can ask, “Are there some conditions under which you can prepare materials that survive that are happy at ambient pressure where you still see this phenomenon?” So the experiments with these hydrogen-rich compounds give you hope that that could be out there, you know?
And you think this is achievable in your lifetime or this is way in the future?
I have no idea. You don't know, but the ability of people to manipulate solids these days is really fantastic.
The scale on which people do things today is just remarkable. So I don't know. It could happen anytime. Yeah.
Well, Professor Fisk, it’s been a delight speaking with you today. I really appreciate our time together.
Yeah. Nice talking to you.