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In footnotes or endnotes please cite AIP interviews like this:
Interview of John Bardeen by Lillian Hoddeson on 1977 May 16,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Systematically recorded autobiographical highlights from childhood through research at Bell Laboratories in 1947-1948 culminating in the discovery of the transistor. Discovery of transistor discussed in detail in fourth and fifth sessions.
We are resuming on May 16 beginning in the year 193 when you made your transition from Gulf to Princeton. You were last time going to tell me what lead to that decision.
As I was saying before, I found the work at the Gulf Laboratories very interesting. It was the early days in geophysics when lots of new ideas were under development and lots of new physics was involved. I realized that if I wanted to do geophysics in the long run I would have to learn more geology. As I said last time, I had been attending a seminar at the University of Pittsburgh trying to keep up to date in the developments in physics in that period.
How large was that seminar?
Oh, it was just the usual seminar, it wasn't very large, at most 8 or 10 people, faculty members from Pit and Carnegie Tech. And a few graduate students. I think Arthur Ruark was the guiding spirit. He was there at that time.
Was your attendance at this seminar supported by Gulf or did you attend on your own time?
It was on my own time, outside of regular working hours. The decision to move on to Princeton was a difficult one, because it was 1933 when jobs were hard to get. I had a good job at Gulf. I didn't know it I would be able to get a good job again if I quit this one to go back to school. But I decided to and I left to proceed with my real interests. And as I said, I was going on my own money so I could pick the University where I wanted to go and I picked Princeton because there was an outstanding mathematics department there as well as the Institute for Advanced Study, that had just gotten started there a couple of years before. They had some of the leading mathematicians in the world and some leaders in theoretical physics.
Did you receive any outside support during any part of your Princeton period?
I got a Fellowship in my second year, but I did the first year on my own. I was there two years. I'd had a master's degree from the University of Wisconsin, and so I did have a reasonably good background in mathematics and physics. I picked mathematics; I joined the mathematics department because I thought my mathematics was stronger than physics. I still wasn't sure I wanted to go into physics. And Fine Hall at Princeton, where the mathematics department was housed at that time, was right near the physics department. And at that time, the Institute for Advanced study was located there. They didn't have their own building at that time.
And physics was then in Palmer?
Yes, that was right next to mathematics and there was a joint break for tea time every afternoon. They'd have tea about 4:30 and the people from both mathematics and physics would come. There was close cooperation between the two departments and also with the Institute for Advanced Study. The people at the Institute gave advanced seminars which were over my head but I went to some of them anyway. In the first year Von Neumann was giving one which I attended. I also attended others. The people in the department I might have been interested in working with were Edward Condon, who was then involved in writing his book on atomic structure which has since become a classic in the field, Condon, Shortley, and Robertson, in general relativity, and Eugene Wigner who was then spending half his time at Berlin. I first talked with Condon about a research problem -- this was the first year I was there. He was involved in his book and had some problems of the kind that would fill gaps in the book. They didn't sound too interesting to me. I also talked with Eugene Wigner, and the sorts of things he was doing sounded more interesting. So I started doing research with him.
How close was your student-professor relationship with Wigner?
It was very informal. There were not very many graduate students there then and there was no difficulty in talking with him. I probably saw him once or twice a week when he was in residence there.
Did Wigner specifically suggest that you work on the work functions of metals?
Well, I had been working in a different area.
In quantum electrodynamics. It didn't look like that work would get too far. I was taking a course in solid state theory and there was a lot of interest at that time in this area at Princeton. Fred Seitz was there; he had been there a year or two before I arrived; he had already essentially completed the research on his thesis and he was continuing on with further problems. That was the time Wigner and Seitz developed their method for calculating wave functions for electrons in crystals in a realistic way--that is making calculations for actual metals rather than the normal type of theory which was just calculating with wave functions which weren't specific to any particular metal. They were able to calculate the binding energy for simple models like sodium and lithium and this was a breakthrough in the theory. It looked like it would open up a new area.
Was it obvious to many people at that time that this work was indeed a major breakthrough?
Well, it was hard to tell how far it would go, but looked like it would be opening up a new area to be able to calculate for actual metals rather than for just idealized metals, and also to calculate the nature of the metallic bond. This happened in the first year that I was there.
Did you get very much involved in the actual details of the Wigner-Seitz work at the time it happened?
Oh, I wasn't involved in that directly. Only afterwards, when I really started working on my thesis on the work function of metals, during the second year I was there.
But the Wigner-Seitz work did help to direct your interest?
Yes, that was the motivating force.
Were you friendly with Seitz in that period?
I knew him very well. We both lived at the graduate college at Princeton. We were very good friends. Also there was Joe Hirschfelder who was working on chemical problems. Wigner later had other students but only during a short time was he interested in solid state problems, 3 or 4 years. He had a number of students; Conyer Herring was another of them. We overlapped one year; he came the second year I was there. I made good progress on the thesis and thought I would stay on another year at Princeton, but then I was offered a Junior Fellowship at Harvard. This was due to the influence of Van Vleck, who had since moved to Harvard from Wisconsin and he knew me from my Wisconsin days.
Before we move on to Harvard, I have a few more questions on the Princeton period. You mentioned the course which Wigner gave on atomic physics and solid state theory. I wonder if you could tell me a little more about that course. For example was there a text. Did you perhaps use the Bethe-Sommerfeld Handbuch article?
Well, it was more his own notes. It gave the general background, the Sommerfeld theory, the Bloon theory, I think even something on alkali halides. So it wasn't confined only to metals.
Did you read original papers in that course?
It was more a normal graduate course. We read review articles rather than original papers. There was no text at that time.
Was this one of the first courses on the new quantum theory of solids in the United States?
It was certainly one of early ones. Van Vleck undoubtedly gave courses, but his interests were more in crystal fields, magnetic properties, things of that sort, that were somewhat different from Wigner's interests. Courses that he gave would be directed more along those lines; energy levels of atoms and crystals, crystal fields, and things of that short. Slater might have given courses too. Certainly he did later, I'm not sure whether he did in that very early period.
I find this particularly interesting. It appears as one of the nuclei from which the field of solid state physics in this country developed.
There were three areas in which it got started in the United States. There were many groups in Europe involved in it but in the United States it was Van Vleck, Slater, and Wigner. Slater was more interested in were magnetic properties, dielectric properties and things of that sort. Van Vleck's book of 1932 was one of the books we studied, but in general it was reading review articles. We talked with people first hand and went to lectures.
About how large was the course?
Oh, not many. I would say there might have been a dozen students there, if that many. A dozen students sitting in, don't think they were all taking it for credit.
And that group included you, Seitz, and Herring?
I think I took it the first year. Herring did not arrive until my second year. I didn't consider myself a solid state theorist. There weren't any solid state theorists at that time. You were in theoretical physics. Theoretical physics didn't begin to split up into specialties until later.
Was the word solid state used at all at that time?
No, not until later. I think use of the words solid state really got started after the War. I don't think it was generally used before the War.
Was there a feeling that this was the beginning of a tremendous new field that would eventually mushroom?
I didn't think it would to the extent that it actually did. There were a lot of good problems to be solved in the field. I didn't feel at all committed to spending all of my time in that field then.
What were some of the other possibilities at that tine for you, areas you thought you might work in at that time?
Well, as I said, I was beginning to work at quantum electrodynamics. There was the problem of all those infinities that you run into in electrodynamics. And I tried summing terms in perturbation theory and things of that sort. We didn't make a whole lot of progress. The key ideas came later.
It was early, granted it was early, but did you happen to study any of the work of Mott, Schottky, Wagner and others in this period pertaining to rectification?
I studied Mott's book which came out later in 1936. I studied it while I was at Harvard.
You mean Mott and Jones?
But then, semiconductor work generally came later for you, is that correct?
Yes, I didn't do anything on semiconductors until after the War.
One other question on the Princeton period. I learned from Jim Fisk about lively exchanges between the groups working then in Cambridge, at Harvard and MIT, and the Princeton group. He recalls visits between members of the Princeton physics department who would come up to Cambridge and members of the Cambridge community who would come down and visit the researchers at Princeton. Do you recall similar exchanges?
There were a lot of exchanges, but they came later. The number of people involved was too small then. In the first year I was at Princeton, it was just Fred Seitz and myself. The next year, there was Conyers Herring but he was just a first year graduate student and wasn't yet doing much in the way of research. And probably similarly at MIT and Harvard, the groups were still too small then in that very early period to provide much in the way of interaction. After I went to Harvard of course, I interacted closely with the people at Harvard, with Van Vleck, and in experimental physics with Bridgman. I also saw the people at MIT frequently.
While you were at Princeton, did you participate in any informal study groups with other students, who were there when you were there?
No, not during that period. There were a lot of seminars given by people at the Institute.
Whom at the Institute at that time did you interact with?
Since I was most interested in the theoretical end, remember most Van Neumann and Veblen. There were others who were more mathematical with whom I didn't interact with very much.
Would you as a graduate student be able to talk with these people at tea?
I'd talk with them. I'd generally show up for the afternoon tea and many of them did. I'd see them on other occasions. I don't think I talked to Van Neumann or Veblen too much. What they were talking about was somewhat beyond me at the time I was taking the seminars. I was just getting a little feeling for some of the ideas that they were talking about. I took a course in General Relativity from Robertson, General Relativity and Cosmology, a very good course. At the time I was at Harvard I was asked if I wanted to give a course in General Relativity and I gave a course using Robertson's notes and Eddington's book.
I'd like to ask one more questions about the Princeton Period. You've mentioned in one of your writings that it was in that period that you first met Walter Brattain.
His brother was a graduate student who arrived the same year I did at Princeton, Walter's younger brother. And I knew him. He was a graduate student in Experimental Physics. I think he was working on problems in the infra-red. I met Walter through his brother in an apartment in New York. I went in to visit him occasionally.
Walter Brattain was, I believe, already in this period working on semiconductors at Bell. The copper oxide work was just beginning. Did you talk about this with him then?
I didn't really talk that much physics with him. It was more of a social acquaintance. I'm sure I didn't get involved in thinking about any problems in semiconductors at that time.
Well, then you went to Harvard.
Then I went to Harvard. One reason for going was I was offered a Proctor Fellowship at Princeton which was their top Fellowship and paid very well, but the Fellowship at Harvard was for three years; guaranteed employment for three years. It paid even better in fact than the fellowship at Princeton, $1,500 plus living expenses at one of the houses at Harvard. At that time that was very good money. So my future would be assured for the next three years there. It would have been more of a gamble if I'd stayed at Princeton.
How did you get the position at Harvard? Do you know who recommended you?
I think probably Van Vleck did.
Was that a position you applied for?
No. They interviewed you. They gave a personal interview. When I got the appointment, I was really overawed by these dignified professors, people who didn't know much about the field I was working in. To get these Fellowships one needs strong recommendations from people who know you and Van Vleck was the only one I knew at Harvard. So it must have been him. It must have been mainly due to his influence.
Do you remember who some of the persons who interviewed you were? Were they in physics?
No, I don't think there was anybody in physics. The Senior Fellows who interviewed me were a very distinguished group. They included Whitehead and Samuel Eliot Morrison. H.J. Henderson was the head of the group at that time. His interest was in medicine. I don't think there was anybody in physics.
How large was the group of Junior Fellows? How many, for example, were there in a given year?
It had just started two years before.
Yes, I think so. There were seven or eight appointed the first year and seven or eight, I think, appointed the second year. I think they hoped to build it up to around 20. It was to average about 20 and I was in the third class with about seven appointed each year.
How many of these sever were in physics?
There were three in physics; Jim Fisk, who was later President of the Bell Laboratories, and Evan Getting, who is now head of the Aerospace Laboratories in California. He got involved in military problems during the war and then stayed in that general area. He was more of an experimentalist. Jim Fisk and I were both theorists. Fisk and Getting both came from MIT. I think Getting came the second year I was there. Jim Fisk, think, came the same year that I did.
What were your responsibilities as a Junior Fellow other than carrying out research?
Well, the idea was to give promising young students free time to do whatever they wanted in their research, so there were no obligations. We met every day for lunch with other Junior Fellows who were from all fields. Once a week there was a dinner at which the Senior Fellows (Professors) were present. It was a lively group of young people. And very stimulating both for the Junior Fellows and for the Senior Fellows.
Did you present seminars to one another in this group, or did that not make sense since you were all from different fields?
When we were together, we talked about work in different fields, about ideas people had in different fields. It was necessarily on a very general level. I think I probably found Whitehead the most stimulating in that group of Senior Fellows at that time. He had a very broad knowledge of practically everything and he had something interesting to say on almost any subject. They weren't pedestrian ideas at all. I think he was very stimulating to all of the Junior Fellows.
Would he come regularly to the dinners?
Yes, he would come regularly to the dinners.
Now your detailed work was with Bridgman and with Van Vleck.
That came later. One of the most important things was that this was the first time that I was in a physics department. Earlier, I'd been in mathematics and wasn't quite sure whether I'd go on in applied mathematics or theoretical physics. There I was attached to a physics department. I knew many of the mathematicians. Carrett Pirknoff was one of the Junior Fellows. His father was a Senior Fellow. We had lots of interactions with lots of the people in mathematics as well. We were in physics but we weren't tied nearly as closely with mathematics as we were at Princeton. We were physically right next to each other and the cooperation was very good between mathematics and physics. In most places it's separated. Mathematicians go their own way and interactions aren't nearly as close. At that time at Harvard, they were reasonably good; interactions between mathematics and physics.
I would like to know some details about the physics seminars at Harvard that you attended in this period and about any courses either at Harvard or MIT.
I think it was mostly seminars and talks.
Do you recall any specific talks that were particularly influential in your case?
Van Vleck gave a course which I took, but I don't think it was just the courses. It was mainly the free time to read widely in physics. At that time it was possible to read all the important papers which came out. There were a few journals like Zeitschrift Fur Physik, and The Proceedings of the Royal Physical Review. You could keep up with what was going on in all fields, which of course is no longer possible today.
Was there a journal club or some other way of discussing these papers amongst your group, or generally with others in the field around you at Harvard?
I think there was just the weekly colloquium. The other was more just informal discussions. Of course the group was much smaller, the department was much smaller, the number of graduate students was much smaller. Now there are all the other graduate students and people on the postdoctoral level.
You mention that you were able to study widely while at Harvard and that these studies included the book by Mott and Jones.
Mott and Jones came out about 1936 and I studied that.
Do you remember some of the other books or papers that you read in that period that made a strong impression on you?
Well, of course there was Bethe's article in the Handbuch der Physik. We all studied that.
Did you study that at Princeton or at Harvard?
Oh probably both. It came out I think while I was still at Princeton. I also studied it at Harvard.
It appears to have had a major impact on solid state theory.
I thought that I ought to try to apply some of those methods that I learned at Princeton to some of the problems that they had at Harvard. Bridgman was making a number of measurements on the properties of matter, on high pressure and so on. The only problem I did there was to try to calculate energy of lithium and sodium as a function of volume and also pressure. Of course I had to finish up my thesis which I hadn't finished before I left Princeton. Wigner was away during the last semester I was there. He was at Berlin during that time so there was no one to check my thesis. One problem was that you're not supposed to work towards a Ph.D. while you are a Junior Fellow. They made an exception in my case; they let me finish my thesis. I think I finished it by about Christmas time.
Who did finally check your thesis ?
Oh, Wigner did. He was back at that time then. The problem was to use Hartree-Fock methods to calculate the surface of the metal, to calculate the distribution of electrons at the surface using many-body wave functions. A somewhat similar approach later led to the paper on the theory of conductivity of monovalent metals, which also used functions which involved many-electron wave functions of the electrons in a crystal. For the surface of a metal, we were dealing with such functions. It is a problem involving all of the electrons in a crystal which we solved by Hartree-Fock methods. In calculating the conductivity of monovalent metals, there is a varying field using the atomic vibrations, the vibrations of the ions which produce a field which is fluctuating in time. I think this is the first application of what people now call time-dependent Hartree-Fock.
It's interesting to me that your interest in surfaces goes right back to your thesis. To summarize then, you worked both in nuclear and solid-state physics while at Harvard.
I was really applying similar methods to nuclei -- to calculating the level density of heavy nuclei which one can treat by many-body methods.
How closely did you work with Van Vleck? For example, on the tight binding work?
I think that's the only paper we worked together on. Most of what I did, I did on my own. I would talk to Slater at MIT, and knew Shockley who was a graduate student there. He was interested in surface problems too. So I met both Fisk and Shockley there. Fisk, of course, I knew well. We had lunch together everyday. I knew him better than most because we were both in physics.
Wasn't Fisk then working in nuclear physics?
He wasn't interested in a variety of problems. I don't think that he was particularly in nuclear physics. He did a problem in nuclear physic for his Ph.D. He was then later interested in problems of concern to biologists, for example, how bats navigate by a sonar type system. I think Fisk was more free ranging than I was. He went from nuclear physics to hearing in bats.
In this paper on the compressibility of Alkali-Halides in July, 1933, I see a trend that seems to be repeated in many of your papers. The work was directly stimulated by experimental results, in this case Bridgman's.
I talked with Bridgman quite frequently about what sort of measurement he was interested in and tried to see whether I could calculate from first principles. It required some semi-empirical theory. He was able to account for the data pretty well.
I see that you were still in direct communication with Wigner in '38. On page 373, there's a reference to Wigner. Would you still send him your work to look at?
I would go to meetings, stay in New York, and usually go out to Princeton and spend a couple of days there. The meetings weren't frequent, maybe two or three times a year.
At the end of this paper you also mention Van Vleck as well as Wigner.
I had more interaction with Van Vleck than anyone else there. He was the first one there who was interested in solid state, and so I'd talk about work with him and did the work pretty much on my own.
You mentioned Shockley. Did you do any work with him while you were in Cambridge in this period?
No, I didn't work with him. I knew him. We went to joint seminars, I talked about his work with him, but we didn't work together. He was a graduate student there, just finishing up his thesis. One problem he was doing then was trying to calculate wave functions for alkali-halides which you usually think are just made up of sodium and chlorine ions, but can also be treated from the Bloch point of view. He happened to treat from the Bloch point of view.
And you discussed this with him?
Yes, I discussed this work with him. And also his work on superstates which he did at that time. He did work which essentially showed that you have bands that cross. From the chemical point of view it corresponds to having dangling bands -- band which are not occupied by two electrons, only one at the surface. They call them dangling bands to represent surface states. And this would occur if in the formation of valence bonds, as they move the atoms together, the bands, say the p-band and the f-band which would cross and form valence bonds, according to the tetrahedral bonds, germanium and silicon. I don't think they were thinking about germanium and silicon at that time. In general, Shockley showed that if you have crossing bands, you can have states at the surface which in chemical language are the extra-orbitals left over. The other valence bonds are filled with electrons.
You also worked on symmetry effects in nuclear energy levels with Feenberg at Harvard.  Was that a close collaboration?
Well, we worked closely together. That was kind of an extension of this work on level density. It took it one step further. In this paper, we calculated the level density for a particular value of the orbital angular momentum. We found the density of states corresponding to j=0, j=1, j=2, etc. Wigner showed that isotopic spin would be a good quantum number. That is, forces between the protons and neutrons (strong forces) are essentially the same except for the extra charge on the proton. And so the isotopic spin should be a good quantum number. So we tried to extend the level density calculation using group theory methods to states corresponding for a given isotopic spin. I think it was too elaborate a calculation for its time even then..
What position did Feenberg have at that time?
I think he was a postdoctoral fellow at Princeton. He got his degree in the early '30s and spent a year or two abroad.
Did you also work on cohesion in this period? That was mentioned somewhat, but I don't see it reflected in any of your papers?
Yes, in the compressibility work. I calculated the energy versus volume of sodium and lithium, which required many hours of work with a hand computer. It could be done very easily now using electronic computers, but the calculations were very lengthy. It turned out that we used the wrong field for lithium. Seitz had published his calculations for lithium using an effective field for the ions which was adjusted to give the correct atomic spectrum for lithium. By mistake, he published the preliminary version of the field rather than the final field he actually used. I used his published version.
Later Conyers Herring found that there was a discrepancy. He was trying to calculate conductivities and in the course of the work, discovered the error.
Was Seitz aware of what he had done?
No, I don't think he was aware of it. Conyers did a lot of digging to find out. I guess Conyers found some inconsistencies and then tried to check the results in Seitz's paper and didn't get the energy levels which were published using the field which was published. So I spent many hours making calculations with the wrong field. One of the interesting things in connection with the calculation of the compressibilities was making an estimate of what pressure would be required in cesium to go from a body centered to face centered structure, which was more of a close packed structure. Hard spheres, for example take up a face centered structure rather that a body centered structure. And so it looked like such a change would come from forces between the ions. We made an estimate of pressure at which we would expect this transition to occur. Bridgman looked for this transition and found one pretty close to under the predicted pressure. This was one of the first cases of being able to calculate a structure change before it was found experimentally.
You mentioned in another interview  and in some of your writings that in 1936 you first learned about superconductivity having read Shoenberg's book, which years later you gave to Leon Copper to read. Was this during your time at Harvard?
Yes, that was when I was still at Harvard.
How did you happen to read the book and would you say this marked the beginning of your since then lifelong interest in superconductivity.
Well, of course, I knew this was one of the outstanding problems, and then Shoenberg's book came out which gave an excellent account of the physics of superconductivity. There was then no adequate explanation. I didn't have any good ideas then. I was just learning what the problems were. It was after I went to Minnesota that I started actually doing some work.
How much work on superconductivity did you do while at Harvard beyond reading Shoenberg's book?
Well, I read other things too but I think that was the most important work. As I said, I was just trying to learn what the problems were and trying to think if there was anything that might explain it. In general, during the period at Harvard, I was able to have time to read widely and not feel the pressure to publish. I could read about problems I wasn't planning to work on, problems in all areas of physics. I was trying to keep up with the literature, read all the important papers. I didn't feel committed to working problems in solid state physics except temporarily at that time.
This is the mid '30s, which was of course a very exciting time for superconductivity.
A turning point occurred in 1935 when the London Brothers came out with their phenomenological theory -- it was the Meissner effect which led to the London Theory. It indicated that you should look for different explanations from one based on absence of scattering of electrons.
I'd very much like to talk to you about work on superconductivity in the '30s but would prefer to reserve that for later on when we discuss your own work on superconductivity that led to the BCS theory. I would like to close our discussion of the Harvard period with a question about Jane Maxwell whom you married in 1938. Was this still during the Harvard period?
We were married in June of my last year at Harvard. I left Harvard in July 1938. I met Jane in 1933 at just about the time that I was leaving Pittsburgh. Then I went back in the summer of 1934 to work at Gulf and saw more of her at that time. I'd get back to Pittsburgh occasionally and we would meet. She was at that time teaching biology at Carnegie Tech, at Margaret Morrison College, then the women's part of Carnegie Tech. Later she took a job in a girl's school, a secondary school near Wellesley, also teaching biology, and so I saw a great deal of her during my last year as a Junior Fellow, since she was working close by. We got married just after I finished my term as a Junior Fellow in July of '38. We took a trip out to the West Coast that summer. I got my first teaching job at the University of Minnesota through the influence of Van Vleck. There were a couple of retirements there. Al Nier was at Harvard as a postdoctoral fellow and as a Minnesota graduate was well-known there. He got one of the jobs and I got the other. So I don't think it was due to Van Vleck's recommendation as far as Al Nier was concerned. They wanted to get him back but I was an unknown. And so it was Van Vleck's recommendation that got me the job there.
Is this a good place to take a break now?
Yes, I think we should continue at a later time.
I look forward to the continuation session. Thank you.
 (With E. Wigner) Phys. Rev. 48 (1935) 84-87 and Phys. Rev. 49 (1936) 653-63.
J. Chem. Phys. 6, 372-78 (1938).
Phys. Rev. 54, 809-18 (1938).
With Lincoln Barnett. AT&T Archive, N.Y. John Bardeen, 5/12/77 & 5/13/77, p. 57