Research-Tony Leggett

A reminiscence from Tony Leggett

2003 Nobel Prize winnerand former faculty member.

Tony Leggett lecturing at the Loomis Laboratory of Physics, University of Illinois, around 1985

(Picture courtesy of the Physics Department, University of Illinois at Urbana-Champaign)

After completing my D.Phil. in theoretical physics at Oxford under the supervision of the late Dirk ter Haar, and spending three years in postdoctoral positions in Illinois, Kyoto and elsewhere, in early 1967 I had to make up my mind as to where I wanted to spend the next few years of my academic career. One place which had made me an offer was the University of Sussex, which had been established a few years earlier and had already acquired a reputation for innovation in its research and teaching structure; this alone made it attractive to me. An additional attraction was that the chairs in experimental low-temperature physics and theoretical nuclear physics were held by two people, Douglas Brewer and Roger Blin-Stoyle respectively, whom I already knew and respected from my Oxford days. So it was not difficult to decide to accept the offer from Sussex,and I started there as a lecturer in theoretical physics in the autumn of 1967.

The next few years were great fun. Like my colleagues, I had what, viewed from the perspective of a major US research university, seems a horrendous undergraduate teaching load, but nevertheless found adequate time to continue the research which I had been doing in my postdoctoral period in low-temperature physics, interacting strongly with the Sussex experimental group in that area and making one or two small discoveries which I found quite pleasing, in particular (with Michael Rice, then at Imperial College) on the anomalous spin diffusion behavior of liquid ³He. However, I also found time to appreciate and gain from the unique interdisciplinary ethos of Sussex at that time. One interesting aspect of the latter was that quite a few people who were full-time members of the Physics department were nevertheless able to spend a large fraction of their time in other fields (and in a few cases eventually migrated full- or part-time to the relevant sister department): Maurice Wilford devoted himself to physics education, Roy Turner and, eventually, Norman Dombey spent much of their time on science policy, and Brian Easlea ended up in history and social studies of science.My thinking about the nature of physics was particularly influenced by conversations with Brian and with Aaron Sloman, who had started his academic career in mathematics and physics but switched his interests to artificial intelligence. This kind of intellectual cross-fertilization was very characteristic of Sussex at that time, and I am sure that I was by no means the only person who benefited from it. It was also during this period, and through Sussex, that I met my future wife, Haruko Kinase, who entered the university in the autumn of 1970 to read international relations and whom I first met in the University refectory.

By the early summer of 1972 I had become somewhat bored with the rather traditional kind of low-temperature physics which I was doing; at the same time, thanks in large part to a mini-series of lectures by Brian Easlea, I had become convinced that the problems in the foundations of quantum mechanics, which I had tended to dismiss as the product of bad philosophy, were in fact serious enough to be worth spending real research time on. I had therefore pretty much made up my mind to work full time on the foundations of physics (a decision which in the event I was able to implement only some years later). In retrospect it is remarkable that this kind of drastic switch of one's research area, which for an assistant professor in a major US research university (and perhaps even for someone at the corresponding level in the UK to-day) would seem like career suicide, seemed not just possible but quite natural for a (tenure-protected!) lecturer at Sussex in those days.

However, it was not to be. Just as I was about to junk my collection of low-temperature reprints, my Cornell experimental colleague Bob Richardson passed through Brighton on a flying visit and told me of the extraordinary results that he and his colleagues had found in their ultra-low-temperature nuclear magnetic resonance (NMR) experiments on liquid ³He.These results were so unexpected and intriguing that my first reaction was that maybe they were the first evidence that under the very extreme conditions of the experiment quantum mechanics was actually breaking down. So I decided that before investing years of my research time in the conceptual problems of quantum mechanics, it might be as well to make sure that the latter was still working!

I have recounted the history of my work on what we now recognize as the superfluid phases of liquid ³He in detail elsewhere [1, 2], so will be very brief: Over the Sussex summer vacation I was able to show that the Cornell results could indeed be understood within the framework of standard quantum mechanics, provided that the state of the system possessed a property which I christened "spontaneously broken spin-orbit symmetry": crudely speaking, the nuclear spins of a pair of ³He atoms must be uniquely correlated with their relative positional configuration. This work was presented by my colleague Mike Richards at the international low-temperature physics conference in August, and drew some attention, but there were various competing theories of what was going on in the Cornell experiments and it was not universally accepted. For the next few months I was mainly occupied with my teaching duties and did not have much time to think further about the problem, but in April 1973, the Sussex Easter vacation, I was able to visit Cornell for the whole month at the invitation of Bob Richardson, and managed in this period to produce a more or less satisfactory "microscopic" theory of the NMR phenomena, which not only explained the existing data but made non-trivial predictions for different types of experiment which were subsequently carried out.This theoretical work is by now more or less textbook material, and was the basis for the award to me, together with Aleksei Abrikosov and the late Vitaly Ginzburg, of the 2003 Nobel prize in physics.

When I look back on this exciting period of my research career, then, apart from appreciating the very substantial help I got in this work from individual colleagues such as Michael Moore and Mike Richards, I am very grateful that I was working in the relaxed and permissive environment that prevailed at Sussex in the early 70's. One point of particular interest in this history is that in trying to understand the Cornell NMR data I deliberately "rushed in where angels feared to tread", since while I knew that there was a very well-developed existing theory of NMR, with large books devoted exclusively to it, I had not read those books and did not attempt to; had I done so, they would almost certainly have sent me off in the wrong direction, since it turns out that in this context superfluid ³He is pretty much sui generis. I am fairly sure that had I for example been an assistant professor at a major US research university to-day, with my eyes fixed on the tenure process a couple of years down the road, I would not have had the confidence to plunge into the problem as the novice I was.This relaxed Sussex ethos persisted for the whole of my fifteen-year stay there;  I would hope that some of its spirit remains even under the altered condtions of to-day.

[1] A.J.Leggett, Nobel Lectures in Physics 2003, Nobel Foundation, Stockholm 2004.
[2] D.M.Lee and A.J.Leggett, J.Low Temperature Physics, in press.

    Professor A J Leggett
    Dept. of Physics, University of Illinois at Urbana-Champaign
    Tel: (217)-333-2077
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