Gabriel Aeppli:
Your willingness to listen to anything, no matter how wrong or incoherent, from an unknown such as myself and to give constructive comments,  singled you out as very special and important among the prominent people I ran into at the time. You were a hugely useful source of advice not only on physics, but also on life. Indeed, one of my favourite quotes from you,  is  'All my friends worry about getting a Nobel prize or two, but all I worry about is getting a cost of living increase from the state of New Jersey'. May you continue a long and healthy life to help others as much as you helped me."
BerkeleyDays   by Morel Cohen.
How Great Events Shaped Our Careers
For Elihu Abrahams at his 80th birthday celebration
Elihu received his undergraduate degree at the University of California, Berkeley, in 1947 and  stayed there for his graduate studies in Physics. I started graduate studies in physics at Berkeley  a year later in fall 1948, meeting Elihu soon after in shared courses.
It was then three years after the end of the Second World War, and physics had become a  popular subject. The dramatically successful roles physicists had played during the war in the  development of the atomic bomb and radar, for example, had brought physics into the public  consciousness, imbuing it with intellectual excitement and a kind of glamour and bringing an  awareness that in doing physics one could have, however remotely, an impact on society.  There was a new interest in supporting basic research by both government and industry; there  was a sense that jobs were available. The “GI Bill”, a federal law which subsidized the college  education of returning veterans made it possible for many to prepare for graduate study who  might otherwise never have gone to college. For Berkeley, the result was a student body of  over 400 in physics. Nevertheless, the classes, though large, were not so large as to seem impersonal. The students got to know each other, and so it was with Elihu and me.
A typical pattern for graduate studies there and then was to take courses, pass the preliminary  exams (fortunately reduced to one in number in our time), pass a caricature of a foreign  language exam, and then start one’s Ph D research. Elihu and I reached that stage at the same  time, the end of the spring semester of 1950.
However, while we were enjoying the intellectual delights of physics and rising to its challenges,  and also enjoying the Northern California climate and the beauty of Berkeley and of the San  Francisco Bay area, the world was moving on. Like World War II and the great expansion of the  interest in and support of physics after its end, the intensification of the Cold War with the  Soviet Union at the end of the 1940’s was to have a major effect on its practitioners,  particularly so for the cohort of students at Berkeley to which Elihu and I belonged.
 Within the United States, the anxiety and uncertainty generated by the Cold War resulted in  over reactions by governments at the state and national level. In California, the state  legislature moved to impose a loyalty oath on all state employees in the spring of 1950. With  Berkeley being a campus of the University of California, all faculty members, post docs,  graduate assistants, and staff members were required to sign it. There was an immediate  strong protest by the faculty at Berkeley, and the faculty senate moved to resist its imposition.  Negotiations between the faculty senate and the legislature proceeded during the spring  semester, leading to an agreement exempting the Berkeley faculty and staff from taking the  loyalty oath.
Thus, when my wife and I, newly married, departed Berkeley in June, all seemed back to  normal. When we returned at the beginning of September, I went immediately to campus to  meet with the professor whom I hoped would accept me as a Ph D thesis student. As I entered  campus, the first person I met was Elihu. After a brief greeting, Elihu informed me that the  agreement between the legislature and the faculty senate had broken down, that the loyalty  oath had been imposed on the university, that all the theoretical physicists in the department  either had resigned in protest or had declared their intention to do so, and that there was no  one to work for. I rushed to see my faculty advisor, Francis Jenkins, gravely uncertain about my  future.
I learned from him that he had been given the task of rebuilding the theoretical group within  the department. To start doing so, he had attended the annual summer school on theoretical  physics that George Uehlenbeck organized at the University of Michigan. There Jenkins met a  young solid state theorist named Charles Kittel, who impressed him and who, chafing under the  unpleasantness of Shockley’s leadership of the theoretical group at Bell Labs, was open to  leaving it. Jenkins arranged an offer of an Associate Professorship for Kittel, who was quite  uncertain about moving out to Berkeley. Jenkins convinced him to come for the fall semester  on a trial basis.
Jenkins encouraged me to talk to Kittel about his research interests and gave me reprints of  Kittel’s recent papers to read. I had had no intention of working in solid state theory. I had  planned to become a particle theorist. My only contact with solid state physics had been an  uninspiring reading course for which a professor of electrical engineering named Silver had  gathered a group of students to work through Fred Seitz’s “Modern Theory of Solids” with him.  [It was some time before I realized how prescient Silver had been.] Moreover, Kittel had
 committed himself only to the fall semester. Despite the uncertainty, there was nothing else to  do. Kittel was the only game in town, so to speak. So, I went to speak to Kittel. He gave me a  problem to do, and I became his student, at least while he was there.
As the only game in town, Kittel attracted six other desperate students: Elihu, Al Overhauser,  Fred Keffer, Harvey Kaplan, Yako Yafet, Jack Tessman, and John Weymouth. He gave each of  them a problem in a quite different area of solid state physics. I had no idea how impressive a  feat that was until I started my own research group. He started a solid state theory seminar  which was quite well attended despite there being no other solid state physicists in the  department, perhaps because of the novelty of the subject for Berkeley. We seven were there  of course, but many faculty members attended and showed interest. Kittel talked himself and  assigned seminar topics to us, which was a bit scary because we had to explain to the faculty  from other subdisciplines matters we barely understood ourselves.
In his assignment of research topics to us and in his organization of the seminar, Kittel displayed  a grasp of the entire subject of solid state physics as it was known then. Elihu worked on lattice  relaxation in ferromagnets. Overhauser worked on electron spin relaxation in metals, work  which evolved into an early study of electron correlation. Kaplan worked on the exchange  integral in ferromagnetic iron. Tessman worked on ionic polarizabilities. I worked on size  effects in metals. I forget what Yafet worked on, something in magnetism, and what  Weymouth worked on. [Perhaps Elihu remembers.] What we discovered only later was that  Kittel was already working on his famous 1953 textbook “Introduction to Solid State Physics”,  consolidating his vast knowledge of the subject, so detailed that it extended to page numbers  of key references.
Our circumstances were clearly much better than they were before Kittel emerged as our  possible rescuer from the devastation which followed the imposition of the loyalty oath, but  uncertainty remained. Kittel left at the end of the fall semester, returning to the Bell Labs, and  we did not know whether he would return. Nevertheless, we seven remained together as a  group, continuing the seminar informally, working away individually on the research problems  he had assigned us, and hoping for his return.
 While back at the Bell Labs, Kittel continued his search for an academic position. Clarence  Zener had left the University of Chicago to become director of the Westinghouse Research  Labs, and Chicago was looking for a senior solid state theorist. Kittel was offered a full  professorship there, and Chicago accepted his condition that he bring there his seven students  from Berkeley, unbeknownst to us. He informed Berkeley of the Chicago full professorship.  Berkeley matched the Chicago offer. Kittel accepted, returned to Berkeley in the summer of  1951, and solid state physics was born at Berkeley.
Upon his return, Kittel resumed teaching and supervising his group of graduate students. We  were now six, as Overhauser, brighter than the rest of us and newly married, had already  finished his thesis, wanting to get on with his life. In addition to these pedagogical  responsibilities, Kittel started building up solid state physics at Berkeley, evidently with the  strong support of the department. He was instrumental in attracting Walter Knight to Berkeley,  he of the Knight shift, and he convinced Art Kip to leave MIT and join him at Berkeley. That  these were the first experimental solid state experimentalists hired reflected Kittel’s conviction  that nuclear magnetic resonance (Knight) and electron spin resonance (Kip) were among the  most fertile techniques then available. Within one year of his second coming, Kittel had  firmly established the nucleus of what was rapidly to become one of the great academic centers  of solid state research.
By the end of the academic year ‘51/’52, we had all finished our Ph. D. research. Elihu had  continued working on ferromagnetic relaxation, his thesis topic, and I migrated from size  effects to ferro-and antiferroelectricity to nuclear quadrupole spectra in solids, my thesis topic.  Now put yourselves in Kittel’s position. Over a period of a year or so, you have to find jobs for  seven students. That would be very difficult now. Fortunately for us, times were different  then. Physics departments were growing, and many of them wanted to create solid state  physics groups, very few of which existed then. As a consequence, we faced a far more  favorable relation between supply and demand in our field than has existed for recent decades.  On a larger stage, the slowing of the exponential growth of science, which had persisted for  three centuries, was still a decade or so in the future. To us, it seemed as though Kittel simply  decided on which available job he should allocate to which student. He had already sent  Overhauser to work as a post doc with Jimmy Koehler at Urbana. He kept Elihu on as a post doc  to work with him for another year at Berkeley. He arranged an Assistant Professorship in the  physics department at Pitt for Fred Keffer, where Fred spent his career. Yako Yafet got a post  doc at Urbana. Harvey Kaplan got a post doc in Slater’s group at MIT. Jack Tessman had a  faculty position at Tufts. John Weymouth went to Nebraska. I went to Chicago with an  instructorship in the physics department and the institute for the study of metals. To  emphasize how different times were then, I had an offer from Chicago three weeks after Kittel  told me that he’d “put me in Chicago”. I’d written only two papers, and there was no interview.  All this took place in June for a job to start in September.
That ends my story of the Berkeley days. Please realize that it is a story, not a piece of historical  scholarship. I have relied almost entirely on my memory, with few attempts to confirm those  memories with documentation. Many details may be wrong. I may have conflated times and  events. However, I do believe that in the main, what I have written conveys the sense of what  it was like for Elihu and myself at Berkeley.
Now let me continue with a few brief remarks about the intervening years. Regarding  recognition received by that group of students, three of the seven, Elihu, Overhauser, and I,  became members of the National Academy of Sciences. Overhauser was awarded the National  Medal of Science. Regarding areas of research, all of us were heavily influenced in our choice of  problems by Kittel’s interests during our early post Berkeley years. One look at the title of  Elihu’s early papers confirms that in his case. Overhauser’s National Medal of Science was  awarded for his discovery of the Overhauser effect, which found very important application in  MRI. Perhaps more significant for me was the influence of Kittel’s style, which emphasized  cutting rapidly to the core of a problem with very simple physical arguments. I see it also in  Elihu as I listen to his comments and questions in seminars. Also, Kittel’s effectiveness in  building up solid state physics at Berkeley has to have been a model consciously or  unconsciously for both Elihu and myself. Elihu has had remarkable success in building solid  state theory here at Rutgers, as all of you know. I was given the responsibility for building up  solid state physics at Chicago a year after I got there. Though it scared me half to death, aware  of Kittel’s activities at Berkeley, I naively thought it was something one does after one arrives at  a place. For Kittel, it was bread cast upon the waters. Fred Reif and Leo Falicov went directly  from Chicago to Berkeley, and Marvin Cohen went there after a year at Bell.
Elihu’s influence on physics at Rutgers has been profound, but there is another channel through  which Kittel and Berkeley have influenced this department. David Vanderbilt and Karin Rabe  also descend from Kittel. Their line of ascent is John Joannopoulos to Marvin Cohen to Jim  Phillips to me to Kittel. Less directly, Joe Sak and Premi Chandra were my post docs, and David  Langreth was a post doc in my group, so they have a collateral line of ascent to Kittel and  Berkeley.
 Now for a brief note on terminology: You will have noted that throughout I have referred to as  “solid state physics” what you all know as “condensed matter physics”. Elihu is not a member  of a “solid state theory” group. I did so in an attempt to be historically accurate. During the  times I have been talking about, the field was called “solid state physics”, and the relevant  Division of the APS was the Division of Solid State Physics. Physicists doing solid state physics  were nevertheless interested in superfluid helium, in some aspects of hydrodynamics, in  neutron scattering studies of liquid structure and dynamics, and in understanding the electronic  properties of liquid metals and semiconductors. The common theme was condensed matter  physics. Accordingly, when I was chairman of the executive committee of the Division of Solid  State Physics, I proposed to the committee that the name of the Division be changed to the  Division of Condensed Matter Physics. The name change was approved by the Division  membership at the 1970 APS March Meeting. That is in part why Elihu is a member of a  “condensed matter theory” group.
Finally, let me comment on my subtitle: How Great Events Shaped Our Careers. The great  events referred to were the end of World War II, the Cold War, the communist witch hunt  during the early years of the Cold War, and the cessation of the exponential growth of science.  Added to this were smaller matters like Bill Shockley’s psychological problems and Clarence  Zener’s departure from Chicago. Were it not for the great events, Elihu and I and the other  members of our cohort would not have become condensed matter theorists. Kittel would not  have gone to Berkeley to build solid state physics there. The composition of the condensed  matter theory group here would be very different. Indeed, the pattern of development of  condensed matter physics in this country and to a lesser extent elsewhere would have been  quite different. One example might suffice. Pseudopotential theory might have developed  later and less effectively. Band gap engineering, central to the semiconductor industry and  dependent in part on pseudopotential theory might have developed later, leading to a different  history of the semiconductor industry.
Warmest congratulations Elihu! I am very sorry that I cannot be present to say that to your  face, but I am very pleased that once again we are together in the same department.