Oral History Transcript — Dr. Conyers Herring
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Interview with Dr. Conyers Herring
Conyers Herring; July 23, 1974
ABSTRACT: From Herring's childhood and early education to his election as department head for the theoretical physics group at Bell Laboratories in 1956. Topics include graduate education at California Institute of Technology and Princeton University; Ph.D. in physics, 1937; early interest in astronomy, wartime work (hydrodynamics of explosions, underwater explosions). Much of the interview is devoted to brief discussions of individual publications; discussion of working environment at Bell Labs and experiences there from 1945 through the 1950s. Also prominently mentioned are: John Bardeen, Felix Bloch, Richard Milton Bozorth, Edward Uhler Condon, de Boer, Peter Josef William Debye, DeMarco, Dutton, William Fairbank, Enrico Fermi, Foner, Frobenius, Theodore Geballe, Gorkov, Gorteov, Holstein, William Vermillion Houston, Josef Jauch, Charles Kittel, Kunzler, Kunzter, Lev Davidovich Landau, Fritz London, Bernd T. Matthias, Robert Andrews Millikan, George Moore, Stanley Owen Morgan, Nichols, Obraztsov, J. Robert Oppenheimer, Gerald Leondus Pearson, Pitaevskii, Maurice Rice, Henry Norris Russell, Frederick Seitz, William Shockley, Shur, John Clarke Slater, Rado Suhl, Dave Thouless, Titeica, John Hasbrouck Van Vleck, Pierre Weiss, Gunther Wertheim, Eugene Paul Wigner, Witteborn, Dean E. Wooldridge, Fritz Zwicky; Zmerican Institute of Physics, Bell Telephone Laboratories Journal Club, Bell Telephone Laboratories Library, International Conference on Semiconductors, Massachusetts Institute of Technology, Physics in Perspective, Reviews of Modern Physics, University of Kansas, University of Michigan Summer Symposium in Theoretical Physics.
Hoddeson:Why don't we start with your autobiography. I see that you were born in New York.
Yes, in a suburb of Schenectady. My father was a physician, who married my mother, who was a nurse, when they were both fairly well along. I think she was about 40. And I was born soon after. We lived in quite a variety of places before I was six. A couple of places in rural or small town New York, and I have all sorts of memories of my early childhood, which go back to about age 13 months, I think, but nothing continuous until 2 1/2 or something like that. Then finally, after a tour through the South — we were in North Carolina for a while, two places and in Mississippi for a while — at the age of 5, I came to Kansas. And that's where I was brought up, in Parsons, Kansas, which is a railroad town of about 15,000 in the southeast corner of the state.
You see, I learned to read at a rather early age. I was just curious about the letters and I asked my parents questions. They answered my questions. It wasn't any specific intent, I guess, at the outset anyway, to teach me to read or anything, but I just started picking things up and they cooperated. And so by the time I was five I could read — well, not quite like an adult, but pretty well, and so when it came time for me to enter school, which I was supposed to do at six, the summer before that my parents wondered, well, what would they do with me in school because I was so advanced?
I was very interested at that time in maps and geography and I studied the Atlas and I traced maps with carbon paper. I even learned some of them so that I could draw just freehand from memory. could draw a pretty good map of the United States. So my parents farmed me out to a school teacher who lived on the block during the summer, and I went down to her for a while, I forget just how often, whether it was every morning or several sessions a week or something like that. My impression of it was that she was teaching me,filling me in on some things I'd need when I went to school, but I think actually the intent was for her to size me up and see where I should go in school. And she came up with the dictum that I should start in the fifth grade!
Hoddeson:So what happened?
So I started in the fifth grade, and that was rugged. I found I could read way better than anybody in the class, but when it came to arithmetic, I was just terrible I couldn't do arithmetic at all. I'd bring home big piles of books, trying to catch up on homework, and the teacher said, Oh, they're not supposed to do any homework. After one semester of that, I dropped out. However, I spent my spare time in that semester studying arithmetic, because the intent was, I'd go back into the 6th grade the next year, which I did. In other words, I didn't lose the year, even though I dropped out for half a year. Oh, I know what it was. I couldn't get credit that way.
I went to summer school over the summer to make up the missed semester, and that went alright. Then I went in the 6th grade, and from then on I had no trouble academically with anything. But of course I did have trouble with some of the bigger kids picking on me and so on. Fortunately, I was physically large for my age, and caught up a little bit sooner than I otherwise might have, and went to junior high school. They had a junior high system there.
Hoddeson:When did you go into physics?
Herring:Oh, that was fairly late. In junior high, I got very interested in electricity.
Herring:That's an interesting question. I think the way it really got started was, I was playing with my friends one day in the summer time, summer vacation, and the telephone linemen were replacing the overhead telephone wires, which had gotten somewhat worn from the weather. And one of my friends said, "Why don't we ask them if they'll give us that used wire?"
I thought oh good gosh, this is completely impossible, they'd never give us anything so gorgeous as that. But one of the boys who was more venturesome than I was — I was always very timid about asking people things — asked them if they would give it to us, and they said sure. So here we had these rolls and rolls of wire, and one of the other boys said, "Why don't we make a telegraph, String up lines from somebody's house to somebody else's and have a telegraph." Again I was pessimistic. I thought, gee, little kids like us would never be able to make a telegraph work, but — we did make a telegraph. I think I said at some stage that I'd eat my hat if it worked, and so the first message that they sent over the telegraph, to my chagrin, was "Eat your hat."
But then I got very interested in electricity, and I got out books from the library on electricity. Somewhere along this stage, maybe even earlier I'd gotten out a lot of books from the library on astronomy, which fascinated me. But anyway I got very interested in electricity, because all the boys were interested in electricity. Radio was just coming in at that time, and we kept trying to make crystal sets. There was no radio station — I guess for a while there was a radio station in the town, but by the time I got engaged in the fabrication of radio sets, that had closed down, I think and the nearest radio station was 150 miles away, and none of the crystal sets we were able to make ever picked up a thing, but we made enormous numbers of different crystal sets.
But the telegraph did work. And my father,— he was a physician, but because of reasons of health, at that time had given up doing regular practice - he was doing roentgenology and laboratory chemical bacteriological work, on a sort of consulting basis for the other physicians of the community. And so he had some items of electrical equipment that came with his X-ray sets. When he changed X-ray sets, he gave me a great big console with some great big AC meters going up to 200 volts and all sorts of things like that. I didn't really make much use of that, but it made a wonderful looking thing for my home laborabory. But I did get a lot of chemicals and things from him. So I was also interested in chemistry and of course like all kids of that age, I got chemistry sets and so on. This would have been about the time I was nine or ten, thereabouts. I remember, in eighth grade science, there was alot of chemistry and so on, and I remember coming in and doing all sorts of lecture demonstrations for the other kids.
But electricity was my big interest at the time. We organized a club called the Young Electricians Club and we got a set of progressive examinations which I made up for the different grades, something analogous to the different grades of Boy Scouts, you know. There was, I forget what the various grades were, third class, second class — then there was amateur, which was higher than that, and then there was expert, which was the highest of all, and I tried to make an expert examination that I couldn't pass myself, and then worked for passing it. So that went on for several years. But you were asking about how I got into physics. During junior high and high school, I was interested in electricity. and then had a growing interest in chemistry.
There were some boys across the alley that were very interested in chemistry and we did a lot of chemistry together, and my father had catalogues from supply companies, and so we'd order: we'd get together big orders for flasks and burners and all sorts of things like that, and send them in — anything we could afford. We bought us a pound of sodium and had a field day with that, including some near accidents. By the time I graduated from high school, I remember I was saying that what I wanted to be professionally when I grew up was either an electrical engineer or a scientist. In fact, I said that in 9th grade, junior high, even, electrical engineer or scientist, but I didn't have it more specific than that. Well, when I entered college, I first had to decide, do I go in the engineering school or liberal arts? See, I entered the university at l4.
I fortunately got a scholarship, because my father had died just the year before, and so my family was essentially penniless. But I got an all-expense scholarship to the University of Kansas. I guess I never very seriously considered going into the engineering school, but I wasn't at all sure what I wanted to major in, whether it would be chemsitry or physics or some other science, conceivably even mathematics, though I'm not sure whether I considered that very seriously, but certainly chemistry I seriously considered. Well, chemistry starting in elementary chemistry and then qualitative analysis. I soon realized I was so slow in the laboratory, and also that in order to major in chemistry, the next thing you had to take was quantitative analysis, which used up all your afternoons in the laboratory. Well, I was very fond of tennis, and the idea of killing all my afternoons with quantitative analysis when I was so slow in the laboratory ruled chemistry out for me. So then I started looking at physics and astronomy. Now, physics and astronomy at that time at the University of Kansas were in the same department, but they were sort of sub- departments, separate.
In other words, my credits for my major would include both astronomy and physics courses, but I'd be working under the astronomy professor and meeting his requirements, rather than under all the physics professors. (There was just the one astronomy professor.) And I thought, gee, I'm interested in astronomy, this professor's a nice guy, and the astronomy requirements are very flexible and the laboratory work's all at night — this is the perfect setup. I figured I'd have more freedom in choosing what courses I wanted and so on than if I majored in physics. So I majored in astronomy. Then when it came to graduate work -
Hoddeson:So you got your BA in astronomy.
My BA in astronomy. When it came to graduate work, I applied to several schools, some of the places that were strongest in astronomy. I applied to Berkeley for a Lick Observatory Fellowship, which is ridiculous for anybody with a fresh BA to apply for, but I thought, well, I'll try anyway because my professor gave me pretty strong recommendations. Then I applied to Princeton which was very strong because Henry Norris Russell was there, and then I applied to Caltech, not in astronomy but in physics. And at that time Millikan was running Caltech, and he liked to get the cream of the crop of graduate students, so he, much to the annoyance of all the other schools would send out his awards of fellowships and assistantships several weeks before any of the other schools. So that's what he did to me, gave me a telegram saying what they would give me, which was I thought a rather minimal sort of assistantship.
He called it a $500 assistantship. Then this was followed up with a letter saying that what for brevity in his telegram he'd called a $500 assistantship really amounted to more than that, because it provided you with meals at the Athenaeum and room at the logee of the Athenaeum, and by standards of what I was paying in Kansas and actually what one could have done in California, this was less than $500 worth rather than more, so I was a little annoyed. But anyway, I'd already sent my telegram accepting, because I knew I had very little chance at Lick Observatory, and we'd gotten grapevine word from Princeton that my chances were not very good there.
So then, after April 1st, came the announcement that I had an assistantship at Princeton, and I was somewhat mad at Caltech. for having conned me into taking this. So anyway, I went to Caltech for a year in physics, and just took the standard — I was just doing first year graduate work, taking courses essentially, and trying to —
Hoddeson:—get the basics?
Herring:Yes, get ready for what they called candidacy. I don't think they had a qualifying exam there, the way they did at Princeton, but you had to take a certain set of courses before you were considered a candidate for the PhD. Or if you didn't take the courses, then for each course you'd have to take an exam to get out of it.
Hoddeson:Who else was there at the time, at Caltech?
At Caltech, there were six of us who came that one year, new that year, and these six were — there were two of us from Kansas actually Ken Crumrine and myself, and a man, I forget where he was from, Chuck Alexander, who died a year or two after he got his Ph.D. Then the other three you would have heard of — Dean Wooldridge, Willie Fowler, and S.Q. Duntley. I don't know whether you go around enough in optics circles to know Duntley, but he's been president of the Optical Society and all that sort of thing. Then, older people there included Louis Ridenour, who was finishing his Ph.D.,and Dick Crane, who was just finishing his and quite a number of others.
A pair that I've always remembered very fondly and still see, Mitch and Zak Slawsky. You know the Slawskys at all? I think they're the only identical twin Ph.D.in physics in the country. They're weird looking people. They're very short, almost grotesquely short, with enormous heads and curly hair and jolly dispositions. They're just wonderful guys. They both work for the government in Washington now. Mitch is one of the rearch administrators in the Air Force, and Zak is in Maryland somewhere. I forget just which outfit he works for. Anyway they're real identical twins. And then there were a number of others. I had for a brief period as a roommate, S. K. Haynes.
I think he went first to Vanderbilt for a number of years. Now I think he's at Michigan State, something like that, still a nuclear physicist, I think. There isn't any point in naming too many of the others, unless there are some famous ones. Bright Wilson was there just the year before I was there, in chemistry. He had left.
Hoddeson:Did you learn any quantum physics there?
Yes, let me go back now to learning advanced physics. My first contact with really advanced physics was between my junior and senior years. I was interested in astronomy, and I'd gotten very interested in learning something about relativity, so first I borrowed my professor's copy of Eddington's Mathematical Theory of Relativity, and decided I liked it, so I bought myself a copy, and I studied it over the summers And then in the fall I gave a course of lectures on it at the university, when I was a senior, my senior year. Then I was so impressed with how much it's possible to learn by studying over the summer on your own that I decided to do the same thing the next summer and learn analytical mechanics. So I took Webster's old book on analytical mechanics and went through that the next summer, translating everything. You see this is a very old fashioned book, dJx/dx plus dJy/dy and all that sort of stuff, and I'd had a course in vector analysis, and I'd been very much impressed with the power of tensor analysis as I learned it in the relativity. So I translated everything into vector and tensor notation as I went, and took my own notes on it, which tremendously facilitated remembering it.
So when I got to Caltech, I figured, well, I probably don't need to take a course in analytical mechanics. Zwicky taught the course at that time, and he was said to be an absolutely terrible teacher, and so I decided, well, I'll put in to take the exam to get out of this. So I took the exam, and I didn't pass it. I was too oriented toward — Zwicky at that time was very interested in solid state, and he gave an example, one of the examples on the exam was a crystal with springs connecting the various atoms. Calculate the elastic constant C 11, C12 and C44. Well C 11, C12, C44 I knew from nothing. I'd been studying astronomy and things like that. So I didn't quite pass the exam, although I made a good stab at it. And now I'm coming to quantum mechanics, In the normal progression of courses at Caltech— they had the three term system — first term, you took atomic physics from Millikan; second term, you took spectroscopy from Ira Bowen; and third term, you took elementary quantum mechanics from Bill Houston. Well, I got through the first of those two, and then came a conflict. Third term, Epstein was giving a course of lectures on statistical mechanics. Epstein was a magnificent lecturer.
I thought, gee, I'd just love to take that statistical mechanics course of Epstein's. The only trouble was, it came at the same hour as Houston's quantum mechanics. So I talked with E. C. Watson, who was the faculty advisor for the graduate students there, and asked him what I should do. And Watson said, "Oh, this is very simple. Here's this course down here that's listed for third term, relativistic quantum mechanics from Oppenheimer."
"Now, I know what you want is elementary quantum mechanics, not relativistic quantum mechanics, but the way Oppenehimer's courses go, nobody every signs up for them, people just come in and audit them. So if you sign up for this course, you'll be the only person signed up for it. If you're the only person signed up for it, he'll have to change the subject matter to suit the class." So I did exactly that. I signed up for Epstein's statistical mechanics and Oppenheimer's relativistic quantum mechanics, and sure enough, when Oppenheimer found that there was this one student signed up for relativistic quantum mechanics, then instead of doing Dirac theory, which is what he was going to do, he did basic quantum mechanics.
He didn't use a text in the proper sense of the word, but he did follow somewhat what were at that time the two most advanced treatments of nonrelativistic quantum mechanics, namely, Pauli's Handbuch article - the famous one - and an article that's less well known, but was somewhat more discursive, by Kramers in the Hand-und Jahrbuch der Chemischen Physik, and fortunately, I had learned German pretty well as an undergraduate. It was still pretty rugged, though. I spent so much of my time in the library reading these articles, particularly the Pauli one, that — as a matter of fact, I don't know whether I read any of the Kramers one at that time. I read it later when I went to Princeton, but I read the Pauli article and studied very hard on that, because Oppenheimer was a very fast, excited lecturer, not nearly as smooth a character as he later became, and it was rather hard to follow his lectures, although they were interesting. So I neglected some of my other subjects and just barely squeaked by in mathematical analysis, but these lectures from Oppenheimer were really quite exciting, because he was really going into the bottom of the subject. He wasn't watering it down any.
And Houston, the man who was teaching the course I whould have been taking, was sitting in on this same course — as were a number of the post-docs and people there. So then, the next year, I didn't even apply at Caltech, I just applied to Princeton, and I got a fellowship in astronomy at Princeton.
Hoddeson:One applied each year? I didn't realize that.
Yes. Yes. So then I went to Princeton and I was in the astronomy department for a year, and that was an interesting experience. The most exciting thing there was taking lectures from Henry Norris Russell in theoretical astrophysics. There were two of us in the class, Louis Green, who subsequently went to, I think it's Haverford. He became a professional astronomer, observational, not a theoretician.
He and I were the two students in this theoretical astronomy course in theoretical astrophysics. And Russell said, "Well, have you read Eddington's Internal Constitution Of The Stars?" We both shook our heads and he said, "All right, that's where we begin." So we went zip zip through Eddington's Internal Constitution of the stars. The idea of the regime was that he would meet with us every Tuesday afternoon for two hours, and lecture at break neck speed,but very polished, magnificent lectures, and you could take beautiful notes on them and everything. I have them somewhere. Then in no time at all, we were going through Eddington's —
Hoddeson:If you wanted to deposit those notes in a historical archive such as the Niels Bohr Library of the American Institute of Physics, historians would be very interested in them. Some time you may come across them...
So it wasn't too terribly long before we were all through with Eddington's Internal Constitution of the Stars and then the procedure was really impressive. We would arrive at the observatory — that is the student observatory, where the classrooms were — at 2 o'clock and Russell would say, "Well, what would you like to hear about today?" And we would think over all the things we'd been seeing in the current astrophysics literature, something like that, and we would say, "Well, we've been seeing these papers of Chandrasekhar on relativistic degeneracy in white dwarfs. We'd like to understand them a little better." Or something like that.
We could name any subject we wanted to, out of the whole literature of theoretical astrophysics. Russell would retire to his office for 15 minutes to collect notes. Then he'd come out to the lecture room and lecture us with great excitement for two hours, with the most gorgeous polished presentation — better than you can get in any textbook or anything.
Hoddeson:What made you switch?
I just got a little disenchanted with astrophysics. The — I guess just some of the personalities I encountered there, and the sort of life they led and so on, seemed to me a little bit too isolated and cooped up. Also, partly, realizing what I could and couldn't do, in the way of a research career. It would be wonderful if I could be the next Einstein and construct the unified field theory that would unify all of gravitation and electricity and everything, or if I could do something big like that in cosmology, but I realized that I didn't have the level of ability that would make it likely for me to accomplish anything of that sort, and if I was just going to do fairly routine work, I wondered if maybe there weren't more exciting things I could be doing than astrophysics. Of course, in astrophysics, the atmosphere now is much more exciting than it was then. At that time observationally things were not developing very fast, and so I looked around. Of course I was at the same time taking some courses in physics. I had a course of sort of selected topics in theoretical physics, or something like that, from Ed Condon, and — oh, incidentally, there was a tremendous contrast between the atmosphere at Princeton and that at Caltech. At Caltech they loaded you up with courses.
I had five courses and lots of problems in all the courses and so on, which I sometimes did and sometimes didn't work. I never was very enthusiastic about working problems. And when I talked to H.P. Robertson as an advisor at Princeton, and asked him about what courses I should sign up for. He said, "Well, anything you want, but under no circumstances more than three," and none of them were problem courses. So let's see, what did I take the first term at Princeton? The theoretical astrophysics, the selected topics in theoretical physics, and probably nuclear physics under Ladenburg. Also, though, Condon got a little informal group together. He thought it would be nice to just shoot the bull a little bit with some of the more theoretically oriented students. And so Fred Seitz, who was a post-doc at that time, had just gotten his PhD, and John Bardeen and myself —
Hoddeson:Bardeen was still a graduate student?
Herring:Bardeen was still a graduate student. He was just finishing his PhD. And John Blewett, you know, now at Brookhaven. He was — I don't know if he was a nuclear physicist at that time, or whether he was in something like atomic spectroscopy or something, anyway, experimentalist, but very bright and very interested in theory. And "somehow I thought there were five of us, but maybe I'm thinking of Condon himself as the fifth — anyway, we would get together, and discuss some exciting topic in theoretical physics. Maybe one of us would make a presentation or something, and we'd discuss it, and then we'd adjourn to the Nassau tavern for beer, for the rest of the evening. We'd do that, I don't know, once a week, once every two weeks or something like that. It was very nice, and Ed was a wonderful person to sort of catalyze interactions like that.
Hoddeson:Do you remember some of the topics that were discussed?
Herring:Not too well. I remember, I think John Bardeen told us a little bit about metal surfaces, which is what his thesis was on, with his theory of the work function, and—
Hoddeson:What was Seitz working on at that time?
Herring:His thesis the previous year had been on the theory of space groups, but he wasn't woking on that at this time. Yes, I remember one of the topics he was working on, although I'm not sure whether he reported it at this meeting, but he worked on it while he was still at Princeton there. This was the theory of the infra-red vibrational spectra of ionic
crystals. There was an experimentalist Bowling Barnes, there, an instructor, who had taken some very detailed infrared spectra of magnesium oxide, and found just scads and scads of peaks, not only the main Reststrahlen peak, but also all sorts of other ones at lower frequencies, and he did this work incidentally with Bob Brattain, who is Walter Brattain's younger brother and who was a graduate student there at the time. And then the question is, well, what are all these other peaks?
And Seitz worked out a theory of how the anharmonic couplings of the vibrations would enable you to get combination frequencies, and so on, and there would be various peaks in the distribution, due to the — what we would now say critical points in the two-phonon spectrum and things like that. So he wrote this elaborate paper on this. He also was working on - after the original Wigner-Seitz work, which as I said was not his thesis, but occurred before his thesis - he went on and did some work on his own on the band structure and cohesive energy of lithium, and then he continued those after he left Princeton and went to Rochester, with lithium hydride and other more complicated crystals.
Hoddeson:Was this your first experience with solid state?
Herring:This was my first — well, first real experience with solid state physics. At Caltech, they used to have three physics colloquia a week. I guess one was called physics and astronomy, but three colloquia a week that essentially everybody went to, and they were pushing solid state somewhat at that time there as Zwicky was interested in it from the theoretical side. He had at that time a hobby horse of his, where nobody else seemed to follow him, and I guess was pretty generally discredited eventually, that crystals, even though they seemed to have a perfect lattice structure with the normal lattice constant, really had essential large scale defect structure to them, not just from impurities, although he was very interested in impurities too, and perhaps what we would now call dislocations and their implications for properties of solids. But his idea was that even an absolutely pure crystal in thermodynamic equilibrium would still get some sort of super lattice where there would be slight misadjustments something like hundreds of lattice spaces apart, and that those were vitally important for some properties of crystals like plasticity. So he had those ideas, and then there was a man named Goetz who had just built a low temperature laboratory, and I remember their tellingus what a nice design they had with
Herring:a particular shape for the ceiling, so when they had an explosion it would blow out only one particular side, because everybody who used liquid hydrogen had explosions in those days. So he was doing cryogenics, and there were one or two other people that were doing experimental solid state work of one sort or another. Houston was a little bit interested in electron theory of metals.
Hoddeson:This is just when all the interesting theoretical developments were coming out.
Herring:Yes. See, this was 1933-34, it was this year, yes. And I remember, Willie Powler and I used to go up and go to the theoretical seminars frequently And because we hadn't had quantum mechanics at the time, it was just complete Greek to us three-quarters of the time But we kept trying to understand what we could, and there were a number of those that were on topics in solid state physics and so on. But I didn't really understand anything or get any grasp of it at that stage. But when I came to Princeton, there were these informal contacts with Seitz and Bardeen, and there was enough going on that I decided I would learn a little solid state physics, so I picked up the Handbuch der Physik and started reading the Sommerfeld-Bethe article and the Born and Geoppert-Mayer and so on. And that for the first time gave me a real orderly comprehension of solid state physics.
Hoddeson:Do you remember what you presented at the informal seminar?
Herring:It was an astrophysical topic, I think simply a little bit about the internal constitution of stars and sources of stellar energy and things like that. I probably presented more topics. That's the one I remember particularly.
Hoddeson:Then you stayed at Princeton for a while and you eventually got your degree. You worked with Wigner.
Herring:Yes. I decided at the end of my first year that I would switch from the astronomy department to the physics department, and try to take a PhD with Wigner in solid state physics.
Hoddeson:What was it like working with Wigner?
Herring:Well, I didn't really see so terribly much of him. At that time, he was only on half time appointment. They had an endowed professorship and they hadn't decided whom
to give it to, so they were using the income from the endowment to hire Wigner for half a year and various other people. He was shuttling back and forth to Hungary, spending the other half in Hungary, except the last year I was there, he spent the other half in Wisconsin. So I talked with him once or twice, and he suggested something having to do with a sort of qualitative understanding of band structure, that I might do, and I worked on that. It didn't look too promising, and by the time I got working on it he was off to Wisconsin, So I corresponded with him by letter and I explained to him why I didn't think this was so good and so on. I was also interacting though with Louis Bouckaert and Ro Smoluchowski: You may remember Bouckaert, Smoluchowski and Wigner, a paper on group theory.
And talking with these poeple just at tea time and so on, I got the realization that the no-crossing rule that von Neumann and Wigner had worked out for molecular spectra - electronic levels of molecules as a function of the nuclear coordinates and other things like that - would have important implications in band structure and vibrational structure, for energy or frequency as a function of wave vector. And I also realized that when you had symmetry degeneracies at certain points of symmetry in the Brillouin zone, and looked at the curves of E versus K, when several of them would come together at one of these degeneracy points, they could go up or down, depending on what was the proper thing for them to connect to elsewhere, and I got very interested in that. And so I did a little work on that during the last semester of my next to last year at Princeton, and it looked like promising pay dirt, and I corresponded a little with Wigner about it. And then, all contact with other people ceased over the summer.
I was spending the summer with my mother on Staten Island. And so just working entirely by myself without a library or anything over the summer, at home, I wrote out my thesis. I came to Princeton in the fall, and had the thing typed up and put it in Wigner's hands and said, "Look, will this do for a thesis?" I had some arguments with him, because some of my conclusions startled him a little bit, and it was finally agreed that yes, it would be acceptable as a thesis.
Hoddeson:You say this was your next to last year You had a year left.
Herring:Yes, well that was my — giving the thesis the finishing touches and passing my final exam. Actually I passed the final and was effectively a PhD as of about January, and I just spent the rest of the time there. I was an assistant. Previous years I'd been on a fellowship, this year I was assistant to Wigner, and I did various jobs helping him with some of his nuclear physics research.
Hoddeson:You got your PhD then in '37.
Hoddeson:And you were at MIT next.
Hoddeson:How did that come about?
Herring:Well, the second semester of '37, I think it was, the second semester of '36-'37, the last semester I was at Princeton, Slater had taken a sabbatical semester and come to Princeton to work. And I realized that Slater's manner of thinking and doing things was very different from mine, and I didn't altogether approve, but at the same time —
Hoddeson:What do you mean?
Herring:Well, it's a little hard to say. I thought alot of his approaches were a little too superficial, as compared with Wigner. But I did realize that here he'd come there for one semester, and he'd written several papers, I thought, boy, if I could learn to write papers like that, that would be something, so I'll go to MIT and study under Slater. Well again, I guess I just don't collaborate terribly closely with people usually. I didn't have really all that much contact with Slater, and what I was doing was quite orthognal to anything that he would have done. So I would go down and talk with him occasionally, but there wasn't really much connection.
Hoddeson:This might be a good time for us to discuss highlights of your published works. (Refer to Herring Publications list—see appendix.)
Herring:Now the first two papers were my thesis. This one (refers to #1) is just a clean mathematical thing developing some properties of irreducible representations
of space groups. It involves a theorem that was first proved by Frobenius & Shur - I think I give a reference to it here. Actually I discovered this by myself and gave a much -for a physicist-a much more transparent proof than theirs which was based on theory of continuous groups but since this was already known I didn't publish my alternative derivation. This is the theorem, that the sum of the characters of the squares of the elements in a given representation is either equal to the order of the group, Zero or minus the order of the group and then just applying that, turning the crank.
The more meaty part of my thesis is really one of the things I am most proud of, of all I ever did, my theorem on what I call the indestructibility of contacts. It applies if you have two bands that come together at some point or on a line in the Brillouin zone, where the degeneracy is not due to symmetry or crossing of things with different symmetry — where there's no symmetry at all. Then no infinitesimal change in the potential whatever can lift that degeneracy. It will move around, but it won't be lifted And there are some further conclusions that one can get that involve detailed reasoning, I didn't give the details here. It's only in my thesis on the number of such contacts in a crystal without an inversion center having to be a multiple of four, which was some of the hardest thinking I ever did in my life. Well, those were the only things I did at Princeton.
Then at MIT, I'd started in working on vibrations of crystals, but I finally decided, well, to get vibrations, I have to know the force constants, and to know the force constants, I have to know something about the origin of the force constants, which I tried to do from electron theory of metals.... the sort of thing people do nowadays. But at that time it was very difficult. And this led me into techniques of band structure, and so my first actual published paper from there was on the orthogonalized plane wave methods:And then at the same time, after I developed that for that purpose, I got a stimulus from my friend Al Hill I called him Gordon at that time -A. G. Hill who's still at MIT, he was an instructor then - he was an experimentalist but he had been working at Rochester on a band structure calculation for beryllium with Fred Seitz, and I pointed out to him, "Look, beryllium is di-valent, you're getting out to the edge of the Brillouin zone, the Wigner-Seitz method alone isn't going to be good enough, why don't we use this ortho-gonalized plane wave method?" We agreed that we would work on this together, and this rather lengthy paper (item 4) was what developed. That was all I did at MIT.
Then I came back to Princeton for a year. This item is work actually I had done at MIT, but I wrote it up at Princeton and published it from there, on the "Character Tables" for the diamond type and close-packed hexagonal space groups. But this was very slow in getting published, even though I submitted it at Princeton. That's all I published there. Then I went to University of Missouri for a year, and — oh yes, at MIT, we'd had a sort of an eating club, a dinner group that hired a cook, and one of the members of that was Myron Nichols, and there were several others who were working with Nottingham there on thermionic emission and so on. And that got me interested in thermionic emission a little bit, and I read some papers and decided that they were of the beam, unsound thermodynamically. And I wrote this little paper on such things as the cooling of the surface when you draw thermionic emission current from it, and the attempt to measure temperature variation of the work functions.
Then came the War, and let's see — I got interested in — I worked mostly on operational research in strategic military problems and things like that. But I did do some physics on underwater explosions, and there are these two chapters in this book here, (The Physics Of Sound In The Sea), I think the editor of that is, the editors are Bergman Yaspan — you know, Peter Bergman, now at Syracuse. Actually though, the most significant thing I did during the War is not listed here. I should have it somewhere, on the hydrodynamics of explosions, under water explosions.
I don't know if I have it here or have it at home. Probably it's still here — yes. Some fascinating effects that come in there — yes. That actually turned out to have quite a bit of influence on the subsequent literature of the subject. When you shoot an explosion off under water, it makes a lot of gas that pushes the water out, and the water has enough inertia so it keeps on going out, even after the inside pressure has sunk to the external pressure. It keeps on going out til you've got a real big vacuum in there, and then the external pressure forces it in again, and it oscillates.
Well, this had been discovered before I got into it, and the physical principles were known. I worked out the mathematical theory to try to compare with some high speed photographs that Edgerton had taken, and there was a discrepancy. It was only 10 percent or so, but I thought, well, the theory ought to be better than that, and I wracked my brains, what could cause the discrepancy. And I finally decided, well, it's because the thing isn't in infinite water, it's only a modest distance below a free surface, and you have to take account of the image. But then when I worked out the mathematics of the image, it turned out that not only was the period altered, which was the effect that led me to look at this in the first place, but the center of the bubble would migrate.
It would sink as it contracted. Then I of course worked out what it would be if it were next to a rigid surface, instead of a free surface, and it goest toward the rigid surface and away from the free surface. And this turned out to be extremely fascinating.
Hoddeson:So then, after the end of the war, I got to working back at thermionic emission, and wrote this review with Myron Nichols on thermionic emission, of which there were two quite different aspects. Chaper 1 was the thermodynamics of it, and that I wrote, and then Chapter 2 and 3 he wrote, and Chapter 4 I wrote, which is the quantum mechanics of it. So those were two very different disciplines. And there was a certain amount of original work in this quantum mechanics, on the temperature variation of the work function. I added quite a bit to the literature. And also some on the — oh yes, the periodic deviations from the Shottky line, that was my other original contribution here.
Hoddeson:Well, I'm wondering whether we should — I won't be able to read all of these papers, and the question is really, how to go about it. I can certainly read the abstracts and skim a lot.
Herring:— I don't know whether it's possible for you to read them piecemeal, because very often they're papers in which the really interesting things are just occasional Places, like for example, in this thermionic emission work, I would say probably if you were to read just a limited protion of that, read this part on the periodic deviations of The Shottky line, pages 249-251.
Hoddeson:I see. Well, maybe we could go through them in that fashion. Then you might get a better feeling for where I might focus. It's very helpful to get your overall summary of a paper.
Herring:Yes. This one is after I got to Bell Labs. The thermionic emission was too, although I worked on that at Texas.
Hoddeson:Now we're into the "Theory of Transient Phenomena" (l99).
Yes. The basic idea of this is just that you get a sort of a wave propagation of the disturbance, with a wave velocity that's different from the particle drift velocity. But nothing fabulously interesting. This is a paper with Charlie KitteI The basic idea is just that when you excite the surface layers of a metal, there's a skin effect. You're essentially radiating into the metal spin waves of a wave length of the order of manitude of the skin depth, and this radiation causes a dissipative effect that broadens your ferromagnetic resonance. And this was the first crude theory of this. George Hado did a more complete theory later. This was the Knight shift — Townes and Knight had discovered this effect, and Townes had put his finger on what the physical cause was. The question was, how do you make a calculation of that in a metal? I used some of my background experience with band theory and so on to make calculations, so they put my name on the paper.
Now, I got interested in sintering. Gee, how did I get interested in that? Oh yes, my work on thermionic emission had gotten me interested in surface structure of metal surfaces, whether they were hill and valley structures or whether they were atomically smooth and so on, and I realized that, as you heat a surface, it will try to come to thermal equilibrium. which does it prefer to do? Does it prefer to be hill and valley, or flat? That got me a little bit interested in migration of atoms and surface tension of surfaces and so on, and I went to some meetings up in Boston somewhere, and made contact with a metallurgist named George Kuczynski who's now up at Notre Dame. So I got interested in sintering in general, and this paper, it's just a short paper and I think you'll find it fairly easy reading, and the results are rather cute. See, it's just three pages. Then I did other things in this field — "Diffusional Viscosity," the idea that the grain boundaries of a solid can be sources or sinks of vacancies if the solid has no sources or sinks of vacancies except at grain boundaries, then if you push on some of the grain boundaries and pull on others, as you would in a sheering type of stress, then the grains can deform their shapes by self-diffusion currents that go from one side to another.
And this can cause the solid to deform. This tied in with certain sintering experiments. Actually, in all this, I'd say if you want a summary of all my work on sintering, the best thing to read is the later one here, — this is a rather long Review article, but maybe half of it is discussion of experiments, maybe you can just sort of skim through it.
Hoddeson:OK, this is the article #24 in the bibliography list.
Herring:Yes. So much for sintering. I don't think you need to read anything more of mine except that. This, #15 is a paper I wrote with Kittel on a sort of a phenomenological theory of spin waves in ferromagnetic media.
Hoddeson:"On the Theory of Spin Waves in Ferromagnetic Media" (1951).
Herring:Yes. This, #17 is a fairly familiar topic by now.
Hoddeson:— "Diffusion in Alloys and the Kirkendall Effect" (1951).
Herring:Yes. John Bardeen had been interested in the Kirkendall Effect, criticizing some papers that Fred Seitz had written, and some of the work I'd done in connection with my sintering work involved the theory of diffusion. And so John asked me to collaborate on this paper. And my one contribution to this paper was Appendix A, which actually has developed into a very well known effect — namely, this is the first time it was pointed out that the relation of the diffusion coefficient, self-diffusion coefficient, as you measure it with a radioactive tracer, to the self-diffusion coefficient of the vacancies involves a so-called correlation factor, and it's the correlation factor in diffusion that was my contribution to this paper. My last stab in the band theory had to do with —
Hoddeson:This is the Paper No. 19 ("Correlation Energy and the Heat of Sublimation of Lithium", Phys. Rev. 82, 1951).
Dr.Herring—yes, the way correlation energy might be changed by effective mass effects, due to the crystal field. It's not a very important thing.
Hoddeson:"Elastic and Plastic Properties of Very Small Metal Speciments," Phys Rev. 85, 1952.
Herring:This is another bit of good luck. The scuttelbutt around Bell Labs mentioned the fact that people studying short circuits in — what were they? Some enclosed pieces of telephone equipment called "channel filters" — had been identified as due to tin plating on some of the electrodes, growing "whiskers," these very fine whiskers of the order of a micron or two in diameter. And remembering some of the things Zwicky had talked about way back at Caltech I thought, well — but tempering this with knowledge, more modern knowledge of how crystal defects occur — I suggested that these whiskers, because of their very small size, might be crystallographically very perfect, and it should be very hard to nucleate dislocations in them. Therefore, they should stand a very large strain before undergoing plastic deformation. And John Galt volunteered to do the experiments, and this was the first report of the high strength of metal whiskers which has become quite an active field since. This (#21) is just a sort of a review article, similar to the stuff in the Thermionic Emission review.
Hoddeson:"Atomistic Theory of Metallic Surfaces," l952.
Herring:Yes, this is sort of pedagogical material. Then, this work with Kittel on spin waves led to a little bit of thinking about — Kittel was also very interested in the nature of the Bloch wall between ferromagnetic domains, and raised the question, shouldn't it be possible to construct a theory of a Bloch wall for an itinerant ferronagnet, instead of for a localized ferromagnet? And so these two papers were an outcome of that. And I would say, rather than read these papers —
Hoddeson:These are #22 and #23 "Engery of a Bloch Wall on the Band Picture, I, Spiral Approach, 1952, and "Energy of a Bloch Wall on the Band Picture, II, Perturbation Approach," 1952.
Herring:—Yes , One could read the corresponding portions of my magnetism book, which summarizes it in a way that I know can be read piecemeal, because that's the way I tried to write the book. That would be the last chapter here, and essentially the first few pages of that chapter.
The part that I liked best about those papers was the physical picture of what happens when an itinerant electron barges through a Bloch wall. Its spin has to rotate, to follow the spin of the domain, from being lined up with the one domain here, to being lined up with the other domain there. What makes it rotate? Well, what makes it rotate is the torque on it, because it responds gyroscopically. What makes the torque on it? Well, the fact that its spin orientation is not quite parallel to the average orientation. An electron moving this way (demonstrates with his hands) if you have magnetizations that are rotating from this into this, an electron moving this way will have a spin that's tilted a little bit this way, relative to the mean, which gives it a torque, you see, like that, which causes the spin to rotate like that, which rotates it around.
Now, if it were moved in the other direction its deviation from the mean would be in the other direction, and I showed that this really made a very consistent theory.
Well, lets go on.
Then came semiconductor transport and phonon drag. Let's see, what is the first thing? I guess my contact with band theory in general led me to make speculations about what might be the band structures of these semiconductors. This was in the days before cyclotron resonance, when nobody knew what the band structures were, and one of the first band structures, I guess the first elucidation, experimental elucidation of what a band structure was, was from measurements of Gerald Pearson on the magneto-resistance of silicon, and this was presented at the Amsterdam Conference on the Physics of Semiconductors, 1954, in which we showed from the magneto-resistance that the conduction band of silicon must have ellipsoidal minima on the 100 axis, with a mass ratio of about five to one. Pearson came — I didn't go to Amsterdam — Pearson came back from Amsterdam all full of glee, and said that he'd reported this, and at the same time somebody had given a paper on the first cyclotron resonance in this, and they had a five to one mass ratio — perfect agreement.
So, one thing led to another, and Ted Geballe had come to the Laboratories and was measuring thermo-electric power of germanium. Don't read the "Theory of the Thermoelectric Power of Semiconductors" (1954) read the review in Halbleiter und Phosophore, which is paper number — where is it?