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Interview of Sunil Sinha by David Zierler on October 15, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Interview with Sunil Sinha, Distinguished Professor Emeritus in the Department of Physics at the University of California, San Diego. Sinha describes how he has been able to keep up his research during the COVID pandemic, and he recounts his childhood in Calcutta where he attended Catholic schools and developed his interests in math and science. He describes his undergraduate education at Cambridge where he became interested is quantum mechanics, and he explains his decision to remain there for graduate work to conduct research on neutron scattering under the direction of Gordon Squires. Sinha explains the centrality of neutron scattering to the development of condensed matter physics, and he describes the opportunities leading to his postdoctoral research at Iowa State. He discusses his work at Ames Lab and Argonne Lab, where he continued to pursue fundamental research on neutron scattering and rare earth materials. Sinha describes his research at Exxon Lab, and the start of the revolution in soft matter physics, and he explains his decision to return to Argonne at the beginning of the Advanced Photon Source project. He discusses his subsequent move to San Diego where he enjoyed a joint appointment with Los Alamos Lab and when he was able to concentrate more fully on teaching after a career spent mostly in laboratory environments. At the end of the interview, Sinha describes his current interest in spin glasses, exchange biases, and jamming theoretical computer simulations, and he explains the reason for the enduring mystery of the mechanism for high-temperature superconductivity.
This is David Zierler, Oral Historian for the American Institute of Physics. It is October 15th, 2020. I'm so happy to be here with Professor Sunil Sinha. Sunil, thank you so much for joining me today.
You’re very welcome. It’s a pleasure to be here.
To start, would you tell me, please, your title and institutional affiliation?
Right now, my full title is Distinguished Professor of Physics (Emeritus), in the Physics Department at University of California San Diego.
And when did you go Emeritus?
In 2017. Three years ago.
And in what ways have you been active with the department since 2017?
Well, actually [laugh] it’s almost as if I never left!
Like so many people. I still have several grants from the Department of Energy and other agencies. I still had a couple of students to get through their PhDs, I still have one. And I have a couple of postdocs. And I go into work every day. Well at least I did, until the COVID hit. And now of course it’s much more difficult. Anyway, I keep going by meeting with my postdocs and my students over Zoom. We're trying to keep our research going. The last six months have been a bit strange, but the three years have been fun, because it’s almost—I see all my colleagues every day, and it gives me something to do—it’s a lot better than staying home and just watching TV all day. [laugh]
[laugh] And Sunil, how are you keeping up with the lab work, in the pandemic? How well are you able to keep things going?
That’s actually a good question, because for a long time, we were not allowed to go in at all to the lab. It was what’s called the red—they were in the red phase, stage red. And now they're in stage yellow, I believe, which is essential labs partially open, essential people allowed to go in. So, you have to petition the chair and the dean saying that this sort of work that’s going on in my labs is essential, and these people are essential to continue that work. And so, I got that permission and my postdocs are going in now almost every day, and my student is going in. You're not allowed to have more than a certain fraction of people on campus. They're very cautious about that. And when we're in the lab, you have to space out and wear masks and gloves and all that sort of thing. They're very particular about that.
So clearly, Sunil, for your research, the laboratory requires in-person intervention. You can’t just have things automated with computers and then data can be analyzed remotely.
In principle you could, with a lot of effort and infrastructure that we don’t have in our lab right now. So, somebody has to go in, and somebody has to make samples. So, you can’t do that on a computer or remotely. You have to go in and in-person make samples, put them on our own x-ray machine, and study how good they are. And the idea is eventually to take them to the national facilities like the synchrotrons or the neutron facilities and to try and get the real experiment done there. Unfortunately, that has taken a big hit, because they closed for a long time, and now they're opening very cautiously, but you're not allowed to go there like I used to go, with my students, to do experiments. Instead, you have to send the samples remotely, and they run them remotely, and you can visualize it on your computer, what they're getting, and you can tell them what to do. But it’s not really possible to do really complicated experiments that way, because it’s too much of a burden on the local people to ask them to do very elaborate things that we would do if we were there.
And so, I think for all this kind of research that I do and many others, what you might call using the national facilities, synchrotrons, neutrons, x-rays, it has taken a big hit, because everything has slowed down. We had national meetings of our interest group—the Neutron Scattering Society—and it was all virtual. All our meetings are virtual and everything. So people keep going, but it’s much slower, more painful, more difficult right now.
Sunil, let’s put COVID out of our mind for a little while and go all the way back to the beginning. First, let’s start with your parents. Tell me a little bit about them and where they are from.
Well, both my parents were born in Calcutta, India. My father was educated in England, and he went to Cambridge. Then he switched and went to Oxford. This was during World War I.
He must have been older when he had you.
Oh yes, he was. In fact, yeah, I came rather late. [laugh] And so he took a degree in classics and then he came home. Nothing to do with science; he was not a scientific person. But he understood the value of a good education. He joined what was called the Indian Civil Service at that time, which the British employed to run the country, administer the country, and he became a magistrate and a judge in India. It’s a long story which I could go into, but maybe [laugh] it’s not too relevant to the thing. But yeah, it’s a long and tricky, interesting story. I have very mixed feelings about a lot of things that he did, but it was different times, you know. You could regard him as being somebody who worked for the British, but on the other hand, I think he was a very honest and straightforward person. He was never corrupt in any way. So, he did pretty well. And then after—
When you say he worked for the British, is that to suggest that he did not have anti-colonialist feelings?
Well, he did, but he couldn't very well take part in demonstrations and things like that. [laugh] In fact, to my horror, I learned that Nehru—you remember—you have probably heard of Jawaharlal Nehru, who was our first prime minister.
So he was involved in a big demonstration, and he was arrested—civil disobedience, they used to call it in those days. And he expected to go to jail. And my father [laugh] was the magistrate he came before, and who sentenced him to jail. And when I found out about that, I said, “Oh no, my god, you didn't!” And he said, “He was such a great man that after independence, after the British left, he called me up and he said, ‘Listen, I was doing what I had to do; you did what you had to do. There’s no ill feelings. And how would you like to be chairman of the governmental central Tea Board?’” And put him in charge of all the organization that is in charge of exporting tea from India. So—
And what was your father’s field, his career? What did he do?
He studied Latin and Greek! [laugh] He wanted me to study liberal arts and things like that, but I was always interested in—ever since I was a kid I was interested in science, in physics. So, he didn't force me or anything. He arranged for me to go to Cambridge and said, “Yeah, it’s one of the best places for physics, so you should go and study physics, if that’s what you want to do.” But he always said, “I want you to have a job when you come back.”
So, he really worried about that—at that time, there were not many opportunities for scientists. Universities were not the greatest places in those days, in India. There were a few institutes, and there was the Atomic Energy Institute in Bombay, which Homi Bhabha had started, and it had a nuclear research reactor and so on. And he thought that it would be best if I studied nuclear physics so I could come back and work there. But when I was a graduate student—in Cambridge, I was an undergraduate, and then I stayed on and did my graduate work there as well. And I—
Sunil, before we get too far afield, let’s go back to your childhood. Where did you grow up?
And what kind of schools did you go to, growing up?
I went to a mostly Catholic school, which was supposed to be one of the best schools in Calcutta. It was an English language, English medium school, and it was run by Jesuit priests, mainly from Belgium. And actually, there was a Belgian priest who was a mathematician there, who was my math teacher. And he was actually interested in cosmology and things like that. And I found him fascinating. And he actually turned me on to the beauty of science and mathematics in many ways. He was very influential in me going into physics, basically. He just loved the subject, and you could see that, and it was very infectious.
I also used to read books. My mother had a lot of—she bought just a lot of popular science books, and they were around the house, and I used to read them. There were books by James Jeans, and so forth, and about the universe and planets and stars and suns. I was just fascinated. I used to go outside and look at the stars. And when I was young, you could see a lot more stars in the sky than you can now. [laugh] It was much clearer, and you could see all these constellations and stars that I could identify. And then I used to fantasize about what kind of beings might live out there. And then of course I used to listen to the radio, and there was-- We didn't have television in those days. And there was all these science fiction things about people from Mars and Jupiter and so on. So, I was quite interested in astrophysics, actually, and cosmology. In fact, I still think that if I hadn’t gone into what I did, I would have liked to have gone into that. But I just didn't think I was smart enough.
[laugh] That you had to be really smart to make any real impact in that field.
Was somebody like a Chandrasekhar a hero to you?
Yeah. When I was in Cambridge, I met Chandrasekhar. I had a long discussion with him, because—he was a very interesting man. He was quite old, then. He had not won the Nobel Prize. I said, “I find it very interesting that you come from a very sort of orthodox South Indian Brahmin family, and here you've been living at the University of Chicago for all these years, for most of your life now, with your wife. Do you ever feel like you've cut yourself off from your cultural roots and so on? How do you feel about that?” And he said, “Yeah, you know, the University of Chicago has been very good to me. They have let me do whatever I want to, and they have been very supportive. And I've had a lot of freedom here to do exactly what I want —I probably wouldn't have been able to do it anywhere else. But on the other hand, life here without all the ceremonies and weddings and festivals in India is like having curry without the spices.” [laugh]
“It’s like warm water.” “In balance,” he said, “I'm not sure it has been worth it. I just don’t feel—I might have enjoyed life in a richer way if I had stayed within my own culture. But I did what I had to do.” And this was before he won the Nobel Prize, so I can understand he was maybe feeling a little depressed or disillusioned. Because in fact, two months later, he actually won the Nobel Prize, and I'm sure he felt differently after that. [laugh] Because he felt it must have been worth it. And I said, “How could you possibly feel that way [laugh] after all you achieved?” Anyway, that’s an aside.
So to go back, I used to read these books on science, and I tried to teach myself—I wanted to understand how Newton came up with his law of gravitation. It wasn’t enough to just talk about apples falling and one over R squared. I wanted to know: how did he actually conclude that the planetary orbits led to his law of gravitation? So, I tried to read Newton’s Principia. I was like [laugh] 13 or something [laugh] at the time. And of course, the original one was in Latin, as you probably know. So, I couldn't understand—even though my father made me take some Latin at school. But anyway, I then got sort of a condensed English version of it and began to slowly understand. Because I didn't actually—I hadn’t had calculus then, but I sort of understood semi-quantitatively what it was like. And then I read a book called Men of Mathematics by Eric Bell. I don’t know whether you have read it.
And it was fascinating. Just reading about Lagrange and Laplace and Galois and Newton and Descartes and Gauss and all these people—it was just fascinating. I tried to teach myself calculus. And I think I sort of learned a little bit. I could pretty much-- So I was a little bit ahead when I actually went to college and took calculus courses. But I just loved that. That all attracted me very much.
Sunil, growing up, how culturally traditional was your family? How much Indian heritage did you have as part of your upbringing?
My family was not at all typically Indian culturally, because my father had been educated, since he was a child, in England, and he was very British in many ways. And so, we spoke two languages at home. We spoke Bengali, which is my language, but my father hardly spoke that. So, we used to speak to him in English. And so, we grew up speaking English—completely bilingual, actually.
And what about your mother? What was your mother’s background?
She was—again, Indian middle-class family. And she married my father when she was very young. She was actually what one might call ahead of her time, because she was a liberated woman. She decided that she would have to do something, because she could see that there were a lot of women in India who were very oppressed and treated very badly, kicked out of their homes if they got pregnant, became homeless, and so on. So, she decided to start like a shelter for these women. And she started a movement called the All Bengal—Bengal is the state in which we lived, of India—All Bengal Women’s Union, with a bunch of other middle-class women in Calcutta. And they started this home for homeless women and orphans, and it became a huge success. In fact, sort of they now have hundreds of—thousands of women have passed through there, and she became very well-known for doing that work. In fact, she and—you've heard of Mother Teresa, right?
So, they were great friends, actually.
Yes. So they used to have lots of [laugh] interesting contacts. And I used to see her when she used to come over to visit my mother. In fact, they had a tradition that on my mother’s birthday, Mother Teresa would come to wish her, at her house—came to our house to wish her—and on Mother Teresa’s birthday, my mother would go to the home that she ran to wish her. So I was in Calcutta one time with my son and a friend of his, who was a neighbor kid that he brought with him from America. And the kid came from a Catholic family. He was quite religious. And I said to him, “Bob, what would you like to see in Calcutta?” He said, “There’s only one thing I want to see. I want to see Mother Teresa.” I said, “No problem, Bob. [laugh] I'll take care of that. No problem.” He said, “When can we go, Mr. Sinha?” I said, “You don’t have to go. She’s gonna come here!” [laugh]
He thought I was pulling his leg, you know, but I knew that that week was my mother’s birthday. Sure enough, she showed up. And you should have seen the look on this kid’s face. [laugh] I've still got a picture of it. He couldn't believe it. Anyway.
Sunil, what advice did you get that convinced you that you wanted to pursue a degree outside of India?
You know, it was sort of a given in my family, because my father had gone to England, and a lot of the kids in my-- I have to say that I belonged to a rather privileged sort of group of people in Indian society. You might call them—it’s the middle class, not super rich, but you might call it educated, Westernized elite, right? And they all used to send their kids abroad for higher education, because that was believed to be the only way that these kids would come back and be successful.
Was your family Brahmin?
No, no. We were not Brahmins. My family was not even orthodox Hindu. They were Hindus in name, but they belonged to a sect of Hinduism called Brahmo Samaj, which—like Rabindranath Tagore was one of the founders of that. They believe in just prayer and a temple, but no idols, no images, and none of the trappings of orthodox Hinduism. But they believed in—they had their religious services. They believed in God and all that. So, it was a very liberal kind of—you might call it almost—I wouldn't call it unitarian, but sort of—a form of Christianity which wouldn't be rigorously Catholic or Protestant but much more free and easy. So that’s what they belonged to.
And had you traveled to the UK before you went to Cambridge as an undergraduate?
Yes, actually, when I was 13, my father got a vacation paid by the company that he worked for, a vacation in Europe. So, he took us—my mother and my sister and myself—to Europe. We did a complete tour of Europe, starting in England and going around the continent of Europe—France, Germany, and Scandinavia—and then coming back to India. So that made quite an impression on me.
When you got to Cambridge, was your intent to pursue a degree in physics from the start?
Yes, yes. You have to choose a major. Actually, first I did—I did my initial part of the degree, which is called a Tripos there—I did it in math, actually. Mathematics. But then I decided, no, I’d really rather go into physics. So, then I switched to physics. In Cambridge, an undergraduate degree is only three years, and then you get your degree. So, the last two years I did physics and got my degree. And it was good enough for me to be accepted into graduate school at Cambridge. So, I just stayed on there, and started working on my PhD.
Sunil, I'm curious—coming from India, with so many of your fellow undergraduates coming from elite schools in Great Britain, how well prepared did you feel, relative to your classmates, with your physics background?
Physics-wise, you mean, rather than socially?
Physics-wise, I didn't feel at all disadvantaged relative to them. No, I don’t recall any struggle compared to my English fellow students, particularly. At that time, Britain still had National Service and most young men had to serve in the military for two years, so a lot of my fellow undergrads were just coming out of the army, for example.
And what kind of physics was most interesting to you, and what were you best at, as an undergraduate, as you were getting this broad-based education in physics?
Well, yeah. A lot of course depended on the lecturers. But I was very interested in quantum mechanics. The summer before I started my degree in physics, I read a book by Max Born on atomic physics. I found that absolutely fascinating, being introduced to the world of quantum mechanics. So, we had all these famous guys giving us lectures—I even took lectures from Dirac, who was quite old then, but gave some lectures really based on his book. There was Pippard, and Ziman, and Sir Nevill Mott. So, it was a very stimulating atmosphere, especially if you were a grad-- If you're an undergraduate, you don’t really notice. You're not sort of part of the intellectual stream. But when you become a graduate student and you sit in on these Cavendish teas and you hear people talking about their research, then you really—it’s very stimulating.
And how well-formulated was your identity as a physicist by the time you ended your undergraduate career? In other words, when you were starting to think about graduate school, did you know what kind of physics you wanted to pursue for your own research?
Not really, no. Not really. One thing comes to mind—when you're talking about how did I feel relative to my co-students—one of the students, undergraduates in the same class as me, was Brian Josephson. And Brian Josephson, as you know, went on to win the Nobel Prize. So, you could tell even in those days that he was different than the rest of us. [laugh]
He was brilliant. And I remember sitting in a colloquium in Cambridge, and the speaker was talking about this famous experiment where you drop a photon from the top of a tower to the bottom and measure the frequency with high accuracy to test Einstein’s theory of gravitation. And he asked a question [laugh] which stopped the lecturer in his—he was just an undergraduate, mind you—stopped him in his tracks. Couldn't answer the question, and then after the lecture, Josephson was up there talking to the speaker, and they talked for like 10 or 15 minutes, and I think actually he got them to withdraw the paper because they’d made a fatal error. They hadn’t taken into account something to do with—I don’t know what the issue was—something to do with temperature differences between the top and the bottom. And the use of the Mössbauer effect; that’s what it was. Anyway, so you could tell this guy was [laugh] extraordinary. So yeah, certainly I didn't feel that I was going to be able to do anything like he was, but—
Did you stay on at Cambridge for graduate school because there was a specific professor you wanted to work with?
No, but just because it seemed the best place for me to get a PhD from, for later, as far as my career would be concerned. It’s a good place to graduate from. And so, I looked around for a professor, and initially, I was thinking of high-energy physics, right? And so, I went to one of the high-energy professors. Very famous, but I forget his name right now. But anyway, and he said, “Yes, I'll take you as my student. Here’s what you're going to have to do.” And he showed me the bubble chamber, and he said, “We analyze—we do these experiments where we take all these bubble chamber photographs, and then your job will be to analyze every photograph and track all the particles and do the calculations from that.” And that seemed not all that exciting to me. A bit tedious, it seemed to me, just analyzing bubble chamber photographs.
So, I decided to look further, and then I found a professor called Gordon Squires. And Gordon Squires was a neutron scatterer. Neutron scattering had just—was still quite a new field, at that time. People had started doing experiments at nuclear reactors that had started up after the war, and some of them were built for research, and neutron beams. And Harwell, which was the British atomic energy establishment, was a place where Gordon Squires used to send his students to do research. And I decided to join his group.
Sunil, just for some historical context here, what were some of the theoretical or experimental advantages or enhancements that allowed for neutron scattering to become a reality by this point?
Well, first of all, people began to realize that it was a tool that could get straight to the heart of many problems in what we now call condensed matter physics. Because it directly measured correlation functions of quantum space time operators that were being calculated for many body systems. For me, it seemed like almost a direct application of quantum mechanics to actual systems. For instance, phonons had been well-known by that time, and Max Born and people had written beautiful long texts on lattice dynamics. But the only phonons that people measured were with light scattering, and ultrasound. So, you measured the very long wavelengths part of the spectrum, but you never managed to see the full dispersion curve of energy versus what we call wave vector, over the whole of reciprocal space, or what is called the Brillouin Zone. And this was predicted by all the theories of lattice dynamics and so on.
But nobody in those days initially, before neutron scattering came along, had ever been able to measure them. So, we didn't even know whether all that theory was correct, although everybody felt it must be, of course. And then after the war these nuclear research reactors began to be built, and scientists like Cliff Shull and Ernie Wollan demonstrated that you could carry out diffraction experiments on crystals containing magnetic atoms (just as people had done X-ray diffraction from crystals, stimulated by the work of scientists like von Laue and the Braggs). This opened up the whole study of antiferromagnetic crystals which could not be explored in detail previously.
Then there were some classic theoretical papers written by people like Leon Van Hove and Placzek, and Halperin and Johnson and others—which showed in detail how you study the dynamics of atoms and magnetic spins in matter by doing inelastic scattering and so on. And then there were these low-flux reactors, which were very difficult to do experiments on inelastic scattering because the intensity was very low. But it slowly began to be possible. Then Bertram Brockhouse demonstrated this by experiments he and his colleagues did at the research reactor at Chalk River in Canada. (Brockhouse and Shull were awarded the Nobel Prize for Physics in 1994.)
For my research, Gordon Squires assigned me a project to measure the phonon dispersion curves of a very common material—copper. Which nobody had measured before. So that was my project, and I eked out the measurements at the DIDO reactor at Harwell very slowly. Because you'd get a few counts per minute, and you'd sit there, and you'd watch these counts come up on the scaling electronics. And luckily there was electronics to record the things. We didn't have to do everything by hand like they did in the really early days. But I found this all fascinating. Computers were being used, and I began to learn programming—I learned Fortran, and I learned how to write codes that would analyze my data and look for peaks in the data, and so on. I think actually at one time I was interested in just using programming to do all kinds of things that occurred to me in my mind, like analyze language or voices and things like that. Which now people do, but in those days, I had this naive fantasy that I could write a code. [laugh] But anyway, I stayed with the project, and I measured the dispersion curves of copper and I got my PhD. [laugh]
Sunil, how was your dissertation responsive to some of the larger theoretical and experimental questions surrounding the world of neutron scattering at that point?
That’s a very good question. So, we had these phonon dispersion curves now, right? So, there are lots of methods—copper, aluminum, lead all began to be measured. Yeah, so what were the big issues? My advisor, who was Gordon Squires, told me that the way to analyze these dispersion curves in terms of phenomenological force constants between atoms, for which he had developed code. So you postulated certain force constants, tensor force constants, between the atoms in a crystal, and then you used Born-von Karman’s theory of lattice dynamics to calculate the formal dispersion curves. And you did a least-squares-fit to the data, and you came out with all these force constants parameters.
But that didn't seem very satisfying to me, because I thought, “So what? I go from one set of numbers to another set of numbers. What is that telling me about the physics of what’s going on in this metal?” And then I began to read more, and I found out that at a more fundamental level, that was governed by the electrons in the metal, and the electron-phonon interaction. And then a thing called dielectric screening, which I began to study and understand. And then I read a paper by a Japanese physicist—rather obscure Japanese physicist—called Tomiyuki Toya. He lived in the northern island of Hokkaido in Japan, and he wrote this first classic paper, which I found fascinating, where he used a simplified theory of the electron-phonon interaction to actually explain, from first principles, the phonon dispersion curves of copper. And he became one of my heroes, because I said, “Ah, now I have a theory I can really interpret my data with and put in my thesis.” Which I did, but I had a big battle with Gordon Squires [laugh] at that time, because Gordon Squires was upset that I gave short shrift to his force constants [laugh] and so on, you know.
But I have to say, in retrospect, I used to have my disagreements with Gordon, but it turned out that what I learned from him about scattering was much more valuable and has stood me in very good stead. I mean, he really understood neutron scattering, the theory behind it, and he was extremely meticulous, and he was a very, very good lecturer, so I learned a lot from him. Anyway—
Sunil, a cultural question at Cambridge—as solid-state physics was developing, at other places, there was a certain hierarchy. So, for example, right at this time, someone like Murray Gell-Mann would derisively call the field “squalid” state physics, right?
Wolfgang Pauli called it “schmutz physics,” right?
What was the status of solid-state physics and neutron scattering at Cambridge? Was it seen there also as a lesser pursuit below the theory?
No. I think only the [laugh] high-energy physicists felt that way. I think the condensed matter physicists felt that their work was as good as anybody’s. And there was Sir Nevill Mott there, discussing at that time metals, alloys, and the metal-insulator transition. And Pippard. Actually, Pippard wrote an interesting article in those days when I was a graduate student, and he called it “The cat and the cream.” Basically, his thesis was that we understood everything that we probably now needed to understand about solid-state physics, and there was going to be nothing new and exciting in the field. And he was of course very, very wrong. [laugh] But he was still a very clever man.
Anyway, so yeah. And then when I was in Cambridge, I met another graduate student called Lu Sham, who later came to San Diego and worked with Walter Kohn to develop density functional theory. Very bright guy. And I was sort of afraid of him, as he was senior to me—he was graduating that year, and I was still a second-year graduate student. Anyway, he very kindly gave me his thesis to read, which was all about the electron-phonon interaction. I learned a lot from that, and about pseudopotentials, and I began to think that I wanted to do theory, now.
I wanted to do theory more than anything else. But I soon realized that it wasn’t easy to get a job with anybody—I wrote to several people who were well-known who were working in the theory of the electron-phonon interaction and all that, said I wanted to work with them. And they were not interested, as I had no credentials in condensed matter theory. So I decided that, well, I’d better stick to experiment and neutron scattering. And actually, I'm glad I did. Although I've dabbled in theory a lot of my life as well.
Sunil, after you defended your thesis, what options were available to you? Did you think about returning to India? Was that something that you considered?
Yes. In fact, I think my family expected it. And so I did. I returned to India with a wife [laugh] and a kid that I had acquired [laugh] while I was a graduate student. We came back on a ship. In those days, we didn't travel by plane. We came back on a boat, which was like having a two-week cruise, actually [laugh] at sea. Anyway, when I got back, I joined the Indian Atomic Energy Commission, which was called the Bhabha Research Center. And I worked there as a junior staff scientist, sort of as a glorified postdoc. And they were all very nice to me. I got to know the scientists there very well. They became my close friends. For life, actually.
And in particular, one of them was a physicist called Venkataraman, and we used to get together and discuss all kinds of ideas about things like electron-phonon interactions, lattice dynamics, and neutron scattering, and so on. And he really was a big influence. And then he was joined by a young, bright guy called Vinod Sahni, who also was very interested in this, and also very bright. In fact, they wrote a book together about lattice dynamics. Anyway, so I found it a very stimulating time, and it was a very good period. And then I decided, “But I can’t—I need to go to America.” I don’t know, everybody thought that that’s the best thing. Then I got this offer as a postdoc at Iowa State.
Why Iowa State, of all places?
[laugh] Because one of the people I knew in Cambridge was a guy called Allan Mackintosh. And Allan Mackintosh was a very well-known condensed matter physicist, solid-state physicist. In those days, it was called solid-state physics. And he had gone to Ames, Iowa, which was actually—although it’s out there in the middle of the cornfields, it has a surprisingly good physics department because of Ames Laboratory, which was given to Frank Spedding by the government after the war, because he helped to purify uranium for the bomb. And so he was the chemist who really helped with the Manhattan Project, and as a reward, they gave him a lab, and he hired some very good people there, very good scientists—physicists, chemists. And they gave him a nuclear reactor also, a pure research reactor. And so, Mackintosh said, “Come and work with me, and you can operate the spectrometer at the research reactor and do your research as a postdoc with me.” So, I did.
I wonder if Iowa was more of a culture shock to you than Cambridge was.
[laugh] Yes, you can say that! [laugh] I remember getting off the plane in Chicago, when we arrived from Europe. We went via Denmark. My wife is from Denmark, and we visited her folks on the way. So we flew from Copenhagen to Chicago, and then from there to Des Moines. Des Moines, Iowa. And Mackintosh picked us up at Des Moines Airport. and as I drove from Des Moines to Ames, all I could see were gas stations and hamburger bars. And I thought, “Oh my god, where have we come?” [laugh]
“What have we done?” But I spent ten years at Ames, and it turned out to be a very useful and happy time, and productive, because there were good people there to interact with and talk to. It was a very friendly place. And Allan gave me a lot of freedom to do what I wanted. And the reactor was—
Did you build your own lab at Ames, or did you join a lab that was already in existence?
So, I didn't have a lab, as such, because the reactor was my lab where I did my experiments. And so, I didn't need a lab—well, we had a prep lab in the reactor building, to prepare samples and things. Ames lab and the neutron scattering facility were run by DOE, the Department of Energy, but we were competing with places like Oak Ridge National Lab—and in those days, I think the High-Flux reactor was just being built—and the High Flux Brookhaven reactor, at which Gen Shirane was running the neutron scattering program. So, it was hard to compete with these groups, but we did a few things and slowly got recognized in the neutron scattering world.
But I remember the thing that I was proudest of was—at that time, quantum crystals were very big when I was in Ames, and so people had talked about solid helium, and the phonons, and there was this question as to whether phonons really existed in solid helium, because solid helium really wants to be a liquid, and it’s only a solid because of the pressure. And if you calculate the potential between the atoms, you find that in the equilibrium structure, the helium atom is at a position of maximum rather than minimum potential energy. So, it’s unstable equilibrium.
And so how could this crystal exist, and how could you have small excursions about an unstable equilibrium point? And then people developed what’s called the self-consistent phonon theory. Well, first of all, they put in anharmonicity and we realized there’d be very large amplitude motion of a light atom, and then they put in—then they did what’s called a self-consistent phonon theory, which is a beautiful theory which essentially says that I'll take into account the fact that it’s moving not just in the pure crystal lattice, but in the lattice that’s already smeared out due to other phonons. And actually that made the lattice stable, and they predicted phonon dispersion curves. And this was very provocative, and I remember the people who did that, people like Nelson Gillis and Tom Koehler, and I had gotten to know them at conferences.
And the thing was, could one measure these? So in order to measure these, one had to grow a single crystal of solid helium. And I had a colleague at Ames, at the Ames Lab, called Clayton Swenson, who was an expert in high-pressure, low-temperature physics. And he said, “Yeah, let’s do it. I can help you grow a crystal.” So he put one of his students on this thing, a guy named Chuck Tilford. And later on, Allan Reese joined us, another student of his, and Costas Stassis, a former student of Shull’s who joined my group. And they developed this apparatus and a little steel bomb where you could pressurize helium, and in it you could solidify helium—well, then we did lots of experiments at the reactor, and we found out that if you got the temperature gradient across the crystal just right and cooled it the right way, you could actually grow a large single crystal. And you could photograph the crystal with a neutron camera. And by golly, you could measure phonons in it. And this was very exciting.
So, we’d be there day and night, you know, measuring these dispersion curves. And we knew that Gen Shirane at Brookhaven was measuring phonons in solid helium, too. But he was looking at the BCC phase—body-centered cubic phase—and we were looking at the hexagonal close packed or HCP phase. So, it wasn’t exactly the same thing. And we were both able to publish. And then we published several other papers. And we got to know—I got to know Shirane. So these people began to slowly recognize that, you know, Ames [laugh] wasn’t just a place in the middle of the cornfields. We were able to do some neutron scattering of consequence there. Anyway, so that was interesting. But the real strength of Ames lay in rare earth research, because the thing that Spedding really was interested in, was rare earths.
What was so compelling about rare earths at this time?
The magnetism of rare earths. And that’s what Allan Mackintosh worked on a lot. And there was a lot of neutron scattering work. At Ames, the scientists there had the ability to grow large, single crystals of these rare earths, like terbium and holmium and erbium. And these were sent to reactors all over the world like Oak Ridge, and the Risø reactor in Denmark where the Danish scientists did beautiful inelastic measurements of the spin waves, and measured the magnon dispersion curves. And also the crystal fields. So, they tied down the magnetism in these rare earths very well. And I did some of that, but that wasn’t my main thing. I wouldn't say that I was a major contributor in that area.
We stuck to measuring phonons in helium and in rare earth metals and some of the beautiful antiferromagnetic structures in the rare earth metals and alloys. With my brilliant student, Nobuyoshi Wakabayashi, we also carried out the first measurements of the spin waves in chromium, in a chromium alloy, after which hundreds of people then did experiments of chromium. Chromium has turned out to be—a crystal of unending fascination to condensed matter physicists. In my spare time I dabbled in theory and published a few papers on the electron phonon interaction and dielectric screening and so-called “first principle” calculations of phonon dispersion curves in various solids. So anyway, ten years passed, and eventually I decided that I needed to go to a different place, because a lot of my friends had left. Anyway, I decided it was time for something new, so—
Did you have graduate students at Ames?
Yes, I did. Wakabayashi was my first student, and I had a couple more.
Were you concerned that when you took your position at Argonne, that you would be leaving the academic life behind?
I was, yes. I was. But I looked—
So what were the circumstances that convinced you that it was worth it, to leave the academic life?
I looked forward to it for two reasons. One was that the time I wouldn't have to spend teaching would free up a lot of time for me to do research. Secondly, I would get a lot more facilities to do the kind of research I enjoyed doing, than I did at Ames. The reactor was bigger, there were more people around them, and so on. And so it was, I think, a good move, and I never regretted it.
And why Argonne, as opposed to other national labs that might have had similar facilities and research programs relevant to your work?
I'll tell you why. Because at Argonne, the neutron scattering program in the solid-state science division—in fact, the solid-state science division director was a guy called David Long Price, who was an Englishman—or Welsh, actually—who had been a fellow graduate student with me in Gordon Squires’ group at Cambridge. So he knew me—we were friends—knew me pretty well. And he said, “How would you like to come and work here at Argonne, and work on the neutron source? We're going to build a fantastic new spallation neutron source, the first and best in the world!” And they were going to shut down the old reactor, which was called the CP-5 reactor there, and they were going to build the world’s highest-flux pulse neutron facility. And so I decided, yeah, that would be an exciting place to go.
So I said—well, there was a lot of—emotionally, it was difficult to leave Ames, where my kids had grown up and friends that you had for ten years. But in the end, we did leave, and went to Chicago, went to Argonne. And I was then made group leader of the neutron scattering group. And then there was a guy called Jack Carpenter, who came to Argonne and was pushing the idea of a spallation neutron source as an alternative to reactors. And so, he convinced everybody that that was the way to go in the future. And he was right! He changed the whole field of neutron scattering. And the first super spallation source was supposed to be in Argonne.
But then there was—I don’t know—there was sort of politics, or whatever it was—the powers-that-be decided that it was going to be in Los Alamos. So, Argonne was cut off—after they demonstrated a prototype source, that became Argonne’s neutron source. Which still did pretty well. I mean, it did amazing things. For instance, the first measurement—the first determination of the crystal structure of a high-temperature superconductor, which was yttrium-barium-copper-oxygen, was done by Jim Jorgensen and his colleagues at Argonne, at IPNS—at the Intense Pulsed Neutron Source at Argonne. So with all that under its belt, it lasted quite a long time. And I was able to do my research there.
One of the things that I worked on (actually unsuccessfully) [laugh] at the time was trying to measure the nuclear magnetic structure of solid helium-3, which was—at that time, people were interested in very low-temperature nuclear magnetism. So, helium-3 was believed from NMR measurements to be an antiferromagnet, at a temperature of the order of a millidegree Kelvin. And the division director at that time was a guy called Priya Vashishta, and he was very excited at the thought we might be able to measure this at the IPNS facility. So we had a team—there was a guy called Kurt Sköld, a very bright experimental neutron scatterer from Sweden, who was spending some years at Argonne. And the low temperature experts John Ketterson And Bill Halperin from Northwestern.
And so, we all had this collaboration to build a nuclear demagnetization facility where we could grow a single crystal of helium-3 and cool it down to a millidegree Kelvin, and then shoot neutrons off of it, without heating it up too much, (because Helium-3 is a big absorber of neutrons) and measure the magnetic structure. And we almost got there. But then we heard that there was a group in Grenoble that had actually beaten us to it. [laugh] So that was that, and we went into doing other things. So I worked on a bunch of other things, for instance the coexistence of magnetic and superconducting order in the crystal ErRh4B4. Anyway, eventually, after many, many years, they shut the IPNS facility down, unfortunately. Well, that’s another story we're getting into, about how the neutron sources slowly have been shut down, so we’re consolidated now to just two in the country.
Did you see these developments, Sunil, primarily as budgetary considerations, or scientific considerations?
The reason for cutting off the spallation source at Argonne? Well, they claimed that it was budgetary considerations, because Los Alamos had this big linear accelerator, right? Which they used for nuclear physics. And that was slowly—they were finding little use for that. So they decided that they could switch and convert that accelerator into a source for generating spallation neutrons. And so it would be much cheaper to convert the LAMPF (it was called LAMPF, that facility—Los Alamos Meson Physics Facility, right?) to convert the LAMPF accelerator into a neutron production source than to build a whole new accelerator at Argonne. And so that was what was decided.
Unfortunately, the problem is the tension between basic research and the defense needs of Los Alamos. So, Los Alamos is funded primarily by the NNSA, the National Nuclear Security Administration—the defense wing of Department of Energy—and I don’t think they were on board with the idea of paying for a big basic research neutron user facility at Los Alamos. So it never really came to be. Again, they had a prototype, just like Argonne did, but that was about it. But later on, later in my career, that facility figured prominently in my career. And I can tell you about that.
Now, by the time you get to the early 1980s, and as you're preparing to leave Argonne—to continue this question about the broader context of neutron scattering, over the 20-something years that you had been involved in it, at that point, did you see, were the major research questions still essentially the same? Or had advances in the field changed those basic questions?
So, to some extent, because after a while, people got used to all the results that were out there from neutron scattering about phonon dispersion curves. People understood that they were there, and if they needed to, they could look up the neutron scattering results. Magnon dispersion curves and spin waves, magnetism, critical phenomena—these were all—neutrons had made enormous contributions to all of these. And actually, to me, the beauty of neutron scattering—and x-ray scattering, too, almost to the same extent—is the way it can get to the heart of things that the theorists actually calculate. Because they calculate things called response functions, or correlation functions, and these are things you can directly measure with these scattering experiments. And these play a very important role in things like critical phenomena or dynamical phenomena of any kind. Or even structural phenomena, where you have disorder and so forth. So, whenever one came across a new problem, one immediately thought, “Oh, what can I—would neutrons or x-rays throw some light on this?” And often it did, and became an essential tool in solving many fundamental problems in condensed matter physics. And I think it continues to be that, to this day.
What was exciting to you, Sunil, about joining the Exxon Lab?
Ah. Yeah, so that [laugh] was a different period. Exxon at that time was wallowing in cash, because oil prices had gone very high, and the company had a visionary CEO. Exxon had a research lab in New Jersey, and he had the idea that they would build a lab out in western New Jersey, which would rival Bell Labs, but it would be in soft matter, in things of interest to the petrochemical industry.
And when did the term “soft matter physics” come into use? At what point did that start happening?
I think around the time Exxon got going. I think they had a lot to do with pushing that term. I would say from the early to mid-80s onwards, these things became known as soft matter.
And so before that term “soft matter,” where would people who were studying things like polymers, for example—what would they have called themselves, or where would they have been situated in departments?
A lot of them would have called themselves polymer chemists. A lot of them would have called themselves—they would be in chemical engineering departments. And some would be in physics departments, but very few. So yeah, Exxon was a very exciting place, because they said the blue skies—whatever you can think of, because we can support fundamental research. They had lots of resources. I mean, they had lots of money. And they built this brand-new lab out in Annandale, New Jersey. And they said, “We just want to hire some of the brightest people, and we want to think outside the box, do whatever is interesting, but it has to be in the general area of soft matter.” So, for instance, if you wanted to do solid helium [laugh] we would have no interest in that, they told me. [laugh] So I got the message.
So within certain research boundaries, the culture there was very much one of basic science. You could pursue what you wanted.
Absolutely. But it only lasted a few years. [laugh]
It only lasted a few years. And that changed rapidly once oil prices started going down and the company wasn’t doing so well. And they changed CEOs, and the new one who came in, he had no sympathy with basic research. And so, I remember one day coming in and finding that they had made the decision to cut our lab in half, and fire half the people! And this was in the mid-80s. And it was a big shock. I was a group leader there, and I had to tell the management which half of my group they could fire. It was terrible. It was an awful time. And then everybody was all depressed [laugh]. The lab was half-empty. It was a depressing place to be.
But still, Exxon was able to support my research very well, which they had—they owned a beamline, a neutron beamline at the Brookhaven reactor. They owned a beamline at NIST down in Gaithersburg, and synchrotron beamlines at Brookhaven and SSRL at Stanford University. And so, we could travel about the country doing neutron and x-ray experiments to our heart’s content, and there were these Exxon beamlines where we could do those measurements. We didn't have to apply for time to other places, for beam time.
So, it was a very privileged [laugh] kind of existence. And it was also very intellectually stimulating, although I had to relearn—I mean, I was basically a-- I was interested in superconductivity and magnetism, and suddenly I had to learn what an olefin was, and understand polymer physics and things like critical micellar concentrations and things like that. But I think it was good for me. It was hard, but I think it broadened me. So, I had—
Sunil, who were some of your key collaborators during your Exxon days?
The key collaborators? Well, there was David Moncton, who joined Exxon before he went on to Argonne to become head of the—to start the Advanced Photon Source there. And David Moncton and I worked together on an experiment at Brookhaven where we—together with our postdoc at the time, David Vaknin, who is now at Iowa State University in Ames, we got the structure, the magnetic-- We demonstrated the antiferromagnetism in the parent compound of lanthanum—you know, the high-temperature superconductor, lanthanum cuprate superconductor. And so that made a big splash. And even though it fell outside Exxon’s guidelines of being soft matter, it got so much publicity that they allowed me to continue doing it.
And in fact, there were several chemists at Exxon, like Alan Jacobson and David Johnston, who were making these materials, because that was still the blue-sky period of Exxon. This was before the big cut, and before the new guy took over and said, “No, you're all going to be working on stuff of importance to Exxon from now on.” So, in those days, we could still do that, and it was very productive and very exciting. So David Moncton was one.
Then in soft matter, there was a bright young guy called Cyrus Safinya. He’s now a very well-known person who does biophysics at UC Santa Barbara. And there was a guy called Keng Liangwho was another x-ray scatterer that had come there. Later on, Keng became director of the synchrotron in Taiwan. And let’s see—well, the person who actually got me to Exxon was Morrel Cohen. You probably—
He was a very famous guy. And he was one of the first people that Exxon hired, and said, “You hire a group of bright people that you know.” And Morrel called me, so I was one of his recruits, actually.
Where did you get to know Morrel?
At Chicago, when I was at Argonne. Because he used to be at the University of Chicago, and he used to come quite often to Argonne as a consultant or to talk to people there. So, I got to know him. I got to know people from other parts of—like Art Freeman from Northwestern used to come, also, and several others. So that was also fun. So at Exxon—let’s see, who else did I collaborate with? Well, there was a famous guy called Bill Graessley, who was a polymer chemist, and he helped me to get started with doing experiments on polymers, actually. I did my first experiments in collaboration with him. And so, he taught me a lot about that. And there were other people—there was David Weitz, who’s at Harvard now. And fractals had just come along, and David was getting a lot of recognition for his work on fractals. And there was Tom Witten there, who was a theorist, and he worked out the theory of diffusion—simulations of diffusion-limited aggregation and fractal clusters.
And so, it was ideal. I thought this was perfect for a scattering experiment. Because, you know, just give me a sample, and I'll go and put it in a synchrotron beam, and we'll get a scattering pattern, and we'll see what a scattering pattern from a fractal looks like. The scattering from fractals turns out to be very simple. It’s a power law. And that summer, at the reactor at Risø in Denmark, collaborating with a couple of Danish scientists called Jorgen Kjems and Torsten Freltoft, we were able to confirm that, on a sample which was a fumed silica gel, called Cabosil, a commercial product. And we were able to develop a simple analytic formula to describe the scattering from the fractal clusters so we could measure not only the fractal dimension but also the sizes of the clusters. And that became a very popular method.
Later on we worked on gold clusters with X-rays at the SSRL synchrotron at Stanford with Dave Weitz, and his student Min Lin. Jorgen Kjems became the director of the Risø National Lab in Denmark, the basic research facility in Denmark. So I used to go to Denmark, also, and work at the reactor there, and do experiments on fractals. So, it was all great. But I decided to leave Exxon after basically 12 years, when the new director called us all in for his annual state of the lab address and said, “It has come to my attention that some of you are still publishing far too many Phys Rev Letters.” And I realized that any place that didn't value [laugh] publishing in Phys Rev Letters was obviously a place where I didn’t belong—actually what he meant was that publishing a Phys Rev Letter doesn't do Exxon any earthly good. Instead, you should be working on things which are of interest to the company. And in a way that’s perfectly reasonable from the company’s point of view, but not necessarily for science.
This is a change, now. This is something where you say, “Time to leave.”
Yeah. And it was. And a whole bunch of people left gradually, over the years, over that period, and all went to other institutions. All did very well, and they established a very distinguished diaspora of Exxon culture which popularized soft matter in America in a way that hadn’t been before. Soft matter meaning not exactly polymer physics, but something between physics and chemistry. And biology. So anyway, when people started leaving and I heard that, I decided, “Well, this is not the best place to be.”
Sunil, had you kept up your contacts with Argonne during your Exxon years? Were you involved and in the loop with what was going on there?
Yes. In fact, I used to even go back there and do experiments at the neutron facility, at IPNS, from time to time. Yeah. And I knew all the people there, in the condensed matter division and in the neutron and x-ray scattering groups.
Now by 1995 when you rejoined Argonne, how well-developed was the Advanced Photon Source at that point?
I actually got there just when they had their first light. They had turned on the synchrotron. That was essentially the 100th year—the centenary of the discovery of x-rays by Roentgen. 1995. That’s the date I joined them, and 1895 was when x-rays were first discovered by Roentgen. So, there were a lot of celebrations at Argonne. APS was a very busy and exciting place, then, and people were getting all the beamlines ready. So, it took a while before all the beamlines were working and everything, but nevertheless there was enough to do. I didn't regret the decision at all to go back to Argonne. In many ways, it was like going home again, because I knew so many of the people in the lab, anyway. Even though I joined the Advanced Photon Source and didn't go back to my old division, which was—the old solid-state division, which then was called the Condensed Materials Science Division—I still knew all those people. So we used to chat scientifically and socially. It was a good time.
In what ways had Argonne changed over the 12 years that you had left?
Actually, apart from the fact that they had the synchrotron, which they didn't have in those days, the neutron source was still going strong there. I don’t think the lab had changed all that much, actually.
And what was your major research agenda during this time back at Argonne? What were you working on at this point?
So, one of the things that I really got interested in was using coherent x-rays. So, at that time, the Advanced Photon Source was what’s called a third-generation synchrotron, which means it has brilliance that surpasses any of the previous synchrotrons. It was equaled by a synchrotron in Grenoble called the European Synchrotron Radiation Facility, and there was a comparable synchrotron in Japan, the SPring-8. These were the highest-brilliance synchrotron sources in the world. Now, there are many more. Anyway, at that time, a high-brilliance x-ray source meant that you could produce a high flux of coherent x-ray photons by suitably cutting down the size of the beam to a few microns and moving it far enough away from the source, meaning the undulator. So the beam that goes through that pinhole is highly collimated, very directed, and is pretty much coherent in the sense that it’s like a laser beam. It causes a speckle pattern when it scatters off something. And you've probably seen these scatter patterns if you shine a laser beam against a wall or something.
Now, this speckle pattern, actually, if you look at the theory of coherent scattering—coherent light—is essentially a fingerprint of where all the atoms are, or where all the things that are scattering are. And as a result, if they move, the speckle pattern starts to fluctuate. And if you measure these fluctuations, you still get what looks like random noise, if you just look at a few pixels of your detector. But if you analyze this random noise in terms of what’s called an autocorrelation function, meaning you correlate the intensity with the intensity at a certain time after that intensity, and sum up over all the initial times, you get something which is directly related to the dynamics of the things that are fluctuating. It’s equivalent to doing an inelastic experiment in a way, but in real time, rather than in energy space.
And so, for very slow dynamics that occur in soft matter—in polymers and things like that—a lot of those motions are on the scale of milliseconds to seconds to hundreds of seconds. And if you convert that to an energy transfer by quantum mechanics, it’s such a tiny energy—if you convert that time to an effective frequency and then convert that frequency to an energy using h omega, you couldn't hope to measure that tiny a frequency with an inelastic scattering experiment. Instead, you measure it in real time. So, this was a technique that was used by people in laser physics for years, since the ‘60s, and it was called dynamical light scattering. Now people began to realize that you could do the same thing with these coherent x-rays, and you could use x-rays to study the slow dynamics of soft matter. And so that’s what we started to do on the beamline at the APS.
Sunil, what were some of the major technical difficulties in this research? What were some of the things that you had to overcome to get to the data that you were looking for?
Oh, there were many. But they were solved very much by the very capable people who were developing these beamlines. One of the main things would be noise and vibrations on those timescales from all kinds of other things. So getting a completely stable setup. Sometimes it was a matter of getting a detector that could read out—you know, we used these two-dimensional area detectors to take all this scattering data at once, and then read it out, pixel by pixel. And I think one of the things was how to read out these detectors very fast. There was a lot of technical development in developing detectors for this purpose. So once the detector technology developed—before that, you could use a single detector and a single photon counter, and put it into an autocorrelator and do the same thing. But that would be painfully slow, if you want to scan large areas of what we call reciprocal space at once.
And so, the best way to do it was to have a detector which could do a fast readout. And these were developed. Steady-stage beamlines were developed. Still lacking in certain capabilities. For instance, you had to have a highly brilliant source. And then at the sample position, if you want to do experiments on a cool sample or a hot sample, you have to have the right temperature control environment. And there’s some experiments, for example, you want to do at very low temperatures, but that capability doesn't exist on these beamlines that use coherent beams. Because it’s very difficult to put low-temperature capabilities onto these beamlines. So there’s still a lot of—I wouldn't say that it’s perfect, but I think people are slowly developing this technique. It’s still relatively new, and I think it’ll eventually become—they have state-of-the-art facilities of this type. They're already building new ones at Berkeley, at the Advanced Light Source, and at Brookhaven, at the new light source there, at the new synchrotron. And in Europe, of course. So yeah, that was one of the things I really did a lot of concentrating on.
Sunil, did you think you were going to be at Argonne for longer than six years?
You mean the second time, or the first time?
The second time.
Yes, I did. I think I thought I was going to be there forever. I mean, until I retired. And in fact, what happened was that the University of Chicago wanted to hire me as like a kind of adjunct professor to have a joint appointment with Chicago and Argonne, and run their facility—they had a consortium of beamlines at the APS, and they needed somebody to be the director of that. And so, they offered me this position.
And just at that time, I had a friend in San Diego who had been my colleague at Argonne. His name is Ivan Schuller. He’s a senior professor here. And he called me up and said, “There’s a new thing opening up here called the LANSCE professorship. And it’s something that Los Alamos wants to fund. They want to put professors at many of the nearby universities who will run research programs at their neutron facility, at LANSCE.” Which was based on the accelerator there, which at that time was still running. “And so, they will pay half your salary so you don’t have to teach for half the year. And they will pay for your travel back and forth to Los Alamos.” And so, at that time, I thought—well, I talked to my wife, and she didn't want to move from Chicago, so I—
Not even to San Diego?
Well, here’s the thing. I don’t think she realized [laugh] what San Diego was. But she didn't want to move. So I said, “Okay, I'm not interested.” But that year, we had a terrible winter in Chicago, a really grim winter, and I began to regret that I had turned down San Diego, when all of a sudden, a few months later, they called me again and said, “Well, we never filled that position. Are you still interested?” And this time, I said, “You bet I'm interested!” [laugh] So that was it.
So eventually—and also at that time—by the way, at that time, APS was also changing management. David Moncton, who was the director of the Advanced Photon Source, left and went to Oak Ridge and became the director of the spallation neutron source there. And Argonne was in a state of a little bit of uncertainty at that time, about its future.
In what ways? More on the science side, or the budget side?
I would say more on the scientific leadership side. So, there were lots of good people there, but a lot of them were very young people. They needed some senior people to—well, there were some people there, but anyway, I decided that it would be best to move. And also, Chicago had this funny thing—they would offer me a faculty position, but they would not offer me tenure. They're very sticky about that, right? Whereas San Diego said, “Of course you'll have full tenure if you come here.” So that took care of one insecurity.
I mean, Argonne is a wonderful place to work, and to me, it’s home, and I don’t know what they would have done with me, but they had a habit of letting s people who sort of got beyond a certain age and were not so productive in research anymore—sort of getting rid of them, unceremoniously. This always upset me a little bit, because—you either had to become a manager—you either had to go into administration—but if you wanted to stay and do science, you couldn't do that after a certain stage—they would say, “Well, this guy’s too old. He’s not so productive anymore. Let’s get fresh young blood.” So, I never knew whether that would happen to me or not. And they told me at San Diego, they said, “You don’t want that to happen to you. Just think of what they did to so-and-so and so-and-so and so-and-so. You better come here.”
So I moved. And I was commuting back and forth between Los Alamos and San Diego, and working at the neutron source there, and also trying to generate momentum to build a new neutron source for them, a new high-intensity neutron source. This was going to be the next generation pulse neutron source to rival the spallation neutron source at Oak Ridge. But it was impossible to convince the NNSA people, who were basically in charge of the Los Alamos budget, to fund such a thing. And DOE, which was funding part of the neutron source, they were not very enthusiastic about funding the source at Los Alamos for some reason.
So, it never got off the ground, unfortunately, although there were some very good people there. And a lot of them then moved to-- Then eventually they decided to shut it down as a user facility, and now it’s there only for defense-related experiments. If you convince them that there’s something vital to military applications, then you can get on the spectrometers there. But everybody—most people began to move from there and move to Oak Ridge, actually, to the spallation neutron source. And so that also ended my tenure.
At that time, there was a takeover of the administration of Los Alamos, which had been operated primarily by the University of California. The new contractor consisted of a multipartite team with the University of California—and several industrial partners involved as well, although I forget the details. And then this new management, they decided they didn't need a LANSCE professor. So they ended my tenure as a LANSCE professor, which was fine, because I had tenure at San Diego. I just began to teach full-time at UCSD and came back here. And then I used to go mainly to the synchrotron sources and to SNS or NIST to do my experiments with my students. That’s what I do now, at least until COVID hit. [laugh]
Sunil, as you were easing back into academic life, in what ways did you have an arrangement to ensure, just as you were concerned previously, that teaching would not negatively affect your research agenda?
Well, teaching does take a lot of time, but I actually discovered I enjoyed teaching. It’s really quite fulfilling to interact with students who really feel that you've stimulated something in them that is worthwhile. And so I've kept those contacts with some of my—even undergraduate students who have passed through my classes, and I enjoyed it. But it does detract from your research. But then on the other hand, you make up for it, because you have graduate students at a university. And then you can leave a lot of the stuff to them that you would normally be doing if you weren’t teaching.
If you're at a national lab, you have to do a lot of things yourself. But here, you can get the students to do those things. So, you have to spend more time teaching, but if you have a good group of students, you can make up for it, to a large extent. But they only become useful after a couple of years. And then of course your job is to try and find jobs for them afterwards. And that hasn’t been easy with the COVID thing, either.
[laugh] Sunil, what was the research that you were doing at NIST? And was this the first time in your career that you had worked there in a sustained way?
You mean when I used to go there from Exxon? Is that what you're asking?
But even since your time at San Diego, as well.
Oh. Yeah. So, I have a great interest in surface and interface structure and dynamics and scattering. And for this, you have to come in at grazing incidence, with a beam of neutrons or x-rays, to a surface, and study either the fluctuations of that surface or the dynamics of those fluctuations. And this was something that had interested me for a long time, even back to my Exxon days, actually. And I had developed a theory of this scattering process. That was one of the things I liked to do, is to develop a theory of scattering for some process that people hadn’t worked out. Most real surfaces in nature are rough, and I was fascinated by seeing these computer-generated surfaces that were called self-affine fractal surfaces by people like Steve Voss and Mandelbrot and so on. These computer-generated surfaces, they looked for all the world like real rough surfaces you’d see under a microscope. Or they looked like landscapes that you'd see out in nature.
In fact, these computer-generated landscapes, fractal landscapes, were in fact used to generate the landscapes for Star Wars, I believe, in the early days, because they were a very convenient algorithm to generate these landscapes. So I wondered, what would you see if you scattered neutrons or X-rays from this kind of thing? And I used the same self-affine fractal algorithm to discuss how scattering would take place from these surfaces. And that caught on, and that became a huge thing. Now there were many beamlines that started looking at what’s called diffuse scattering, not specular reflection from a surface, which tells you details about the fluctuations on the surface. And these were some of the experiments I was doing at NIST in collaboration with the people there.
And lately, what I've been doing there is to look at some magnetic materials. Then I went through a phase where I was also looking at lipid films. That was my foray into soft matter, which continued after Exxon. So I worked a lot on lipid bilayers and multilayers, and we studied some of those at NIST with neutrons. And I'm planning to do more of that. Also, lately, there’s some sort of disordered crystals where we can use NIST’s enormously high magnetic field, which you can apply to the sample in a neutron beam, and study the small-angle neutron scattering from those samples to look at a phase—there’s a famous phase called the Griffiths phase, which says that in a material with disorders or defects, which wants to order, several degrees above the ordering temperature, there appears a mechanism where clusters of spins seem to form. You can see these clusters with scattering experiments. So we think we've seen that, and we're going to study that further. So it’s a variety of things we can do at NIST, ranging from soft matter to hard matter to superconducting films. There’s a whole bunch of things.
What about x-ray research? Did you pursue much x-ray research at NIST as well?
There are no x-rays at NIST.
There are none, okay.
It’s not a synchrotron. Well, there are x-rays, but it’s the same kind of x-rays that I could get at home with our x-ray machine. They use it to characterize samples. But they don’t use it as a research facility.
And so this is to say that your most recent research on x-rays has taken place in San Diego.
No. It has taken place at places like Berkeley, at the Advanced Light Source. At Argonne, like places like the Advanced Photon Source. And at Brookhaven, at places like the National Synchrotron Light Source II—the new version of it. And the most exciting thing we've been doing for the last few years in synchrotron work has been looking at spin glasses. This is an old problem. Because I'm old, I go back and look at old problems that never were solved, right?
And this was a problem that the theorists ran away with, and they used it to develop algorithms that now work for things like protein folding and neural networks and all kinds—it had huge impact on all kinds of things. Experimental problem of whether there really is a spin glass second-order—a true second-order transition from a disordered fluctuating phase to a static disordered phase, which is a very novel kind of phase transition, and fascinated the theorists as a result—has never been really verified, because you can’t do a scattering experiment on it, because the time scales are too slow.
So, I realized that this was an ideal thing where we could use this technique of dynamical x-ray scattering that I talked about, which we use for soft matter, to study these magnetic disordered systems called spin glasses, and watch them as they go from the paramagnetic fluctuating state into the frozen spin glass state. And lo and behold, we were able to see this beautifully—this critical behavior that had been predicted but not seen. And so that’s one of the things that I'm planning to do more of. Just disordered and—there’s all kinds of really interesting new systems, like they call them spin liquids—quantum spin liquids, spin glasses. This whole family of materials I think is—a lot can be contributed to by these kinds of experiments. So I think if I was a young man and had the energy and the time, I would go after that for the next 20 years. [laugh]
But I don’t have that kind of time.
Sunil, just to bring the narrative up to the present, even amid COVID, what have been the research projects that you've been working on and have been of most interest to you in the past few years?
Well, this spin glass project is one. The other one is a phenomenon called jamming, which is another theoretical computer simulation. People say that things—how things moved when they're jammed, like in a sandpile, or in grains that are packed together, or in a traffic jam, they can’t move freely, right? So they can only move when there’s a space to move into. And this kind of dynamics has a very different kind of dynamics to ordinary fluctuation dynamics. And it’s called jammed dynamics.
I thought this would be a nice system to study, and the system we chose was magnetic domain walls. When a system orders magnetically, the domains fluctuate and grow until finally they become infinitely large and freeze, and that’s the new magnetic ordered state. Well, if you have a finite sample and several different domains start growing with different symmetries, they can’t all become infinite at the same time, so they jam up against each other. Then the dynamics of the domain walls is jamming dynamics. And we were able to see this in a synchrotron experiment. And so we published that. So that’s one of the things that I've been interested in. Random disordered magnetic systems.
I've also been working on exchange bias, which is something that my colleague Ivan Schuller was one of the pioneers of. And there was another professor here who unfortunately passed away called Ami Berkowitz who also collaborated with me on that. And exchange bias is the thing that’s—it’s the mechanism that’s used in everybody’s disk drive, in your computer’s disk drive, to read and write bits of data on a magnetic disk. And the way it works is that you have a magnetic field, and a magnet that flips back and forth as the bits fly by underneath, responding to the magnetic field or the bits. But this has to be supported on something else which is magnetic that holds it there, and you can’t have that one flip back and forth as well, because then you'd lose the signal. And so, there’s a phenomenon called exchange bias which says that if you put an antiferromagnet next to a ferromagnet, which is what the read head is—if you put an antiferromagnet there, it blocks it from flipping.
So, you want to study the interfacial magnetism of these systems, to study what’s going on really at the interface. How is it blocking the movement of the domains underneath? And so, we did a number of experiments of that kind at Berkeley, at the Advanced Light Source, and at Los Alamos, at the neutron source, before it shut down. So those are some things. These lipid systems, I'm working with my students to try to put nanoparticles into lipid to make composite systems of nanoparticles and lipids or polymers, and to make new functional materials out of those. Because, for instance, if you can arrange for the nanoparticles—let’s say gold nanoparticles—to form, you can coax them to form a lattice inside these structures; then they act like photonic crystals, and they can reflect light in different colors, and you can manipulate that with electric fields and magnetic fields. So a lot of interesting potential there. And then there’s the spin glass problem, of course, and that I plan to do more of. So, it keeps me busy, and keeps my students busy.
Good. [laugh] Well, Sunil, for the last part of our talk, I want to ask a few broadly retrospective questions about your career, and then something forward-looking. I want to come back—I was struck by your obvious reaction at Exxon, where the new understanding was basic research is sort of ending, and if you want to do research here, it needs to be specific to the company’s bottom line. It’s so obvious, listening to you talk about your career, that your first priority has always been basic science, and understanding and advancing the research. But I'm curious in what ways, if at all, your research has had commercial viability. If you've ever pursued various ways that your research is relevant to commercial applications or applications beyond the purely academic pursuit of understanding the physics?
Yes, there have been a few cases like that. For instance, I was hired as a consultant by a couple of companies, one not far from here in LA, and one up in Silicon Valley. Well, one of them was interested in x-ray mirrors, and producing x-ray mirrors. This was for some kind of defense application which I can’t go into. But anyway, they read that I had done some work on the scattering of x-rays from surfaces, from mirrors, and they wanted to know how much that roughness or diffuse scattering from the surface would affect the performance of their devices. So, they asked me to come and give them some lectures on that and do some experiments that would help them choose the right materials or process the right materials to develop those things.
And then the company in Silicon Valley is a company that looks at chips, electronic chips, that are being developed now. When chips are made, actually, they need to be characterized. And the way they characterize a lot of these things is as they come off the assembly line, they have an x-ray beam that just essentially scatters off these chips, because they have certain periodic structures on them that give you reflections, and you can characterize—sometimes you can even get images of the chips this way. But what they were interested in is defects, right? Like roughness and so on. Can one characterize those on the chips in a quantitative way? And that’s exactly what my theory of x-ray scattering from rough surfaces does. So they wanted me to generalize that to looking at three-dimensional chips, and see how that theory could be applied to—they had machines—this company actually makes x-ray machines that can scan these chips and collect a lot of information, from which they can get a lot of structural information about the chips. But they wanted to know specifically, could I help them develop algorithms whereby they could develop models for the defects in the chips? And so, I did that to a certain extent, with them.
But I haven't actually—I mean, it’s one of those things that would take a lot of effort, which I don’t have the manpower for anymore, to write the code that would actually do this in a full three-dimensional chip. I don’t know if they're doing it now themselves, or whether it’s one of those things that still remains to be done. But if I had a student, I could get him to work on this problem and the company would probably pay quite well for him to develop this code. But I don’t take students anymore, and they're all graduating, so I don’t have that manpower anymore. [laugh]
Sunil, given your long career in the field, and given that you've been present at the creation for so many of these fundamental developments in both condensed and soft matter physics, I wonder if you can reflect on things that are now truly understood that weren’t in the 1960s, and things in the field that remain mysterious, that remain—despite all of the advances in the technology, the instrumentation, the experiments, and even the theory—those issues that were mysterious in the 1960s that remain mysterious today?
Well, for the latter, one of the biggest examples that comes to mind is the mechanism for high-temperature superconductivity. Right? I mean, there’s no universally accepted explanation right now, although there are very gifted people who have come up with plausible theories. But they're very controversial, still. So, I don’t think there’s any accepted explanation for that. And so, I think that’s one big example about something that’s not completely understood to this day, even though there has been more than 20 years of intense research on the subject.
Other things in the ‘60s that people didn't understand is the importance of topological physics, and the importance of topology in determining certain properties of a material which are what one might call—because they're topological properties, they cannot be changed easily by defects or something like that. They belong to a geometric property of the thing. That realization came along after the 1960s, I would say.
Then what else? I guess there are lots of things like a lot of what we understand about magnetism and the magnetic excitations in solids, and spin waves, magnons, itinerant magnetism and so on, that has all come about because of experiments done since then. And if I look at soft condensed matter, I would say—I'm trying to think of things that we now know—well, the idea of fractal structures was not appreciated very much or known in the ‘60s, or even thought of. And I would say the study of disordered materials in glasses. The glass transition is another one of those really important problems that still has not had a complete solution, like high-TC super—I would say that—so high-temperature superconductivity and the theory of the glass transition are things we still don’t agree upon that we understand them very well. At least in condensed matter physics.
Sunil, for my last question, I want to look ahead, and I want to bring it back to when we were talking about your career as a student and your early interest in particle physics and astrophysics. There seems to be a trend in physics generally toward convergence, right? That astrophysics and cosmology are becoming increasingly unified, and particle physics is becoming increasingly unified. As the field in general moves toward a level of convergence, where do you see soft matter physics and condensed matter physics fitting in to this broad-range goal of unifying all theories in physics?
Let’s put it this way—soft matter physics and current condensed matter physics uses, at least the theoretical part of that, uses an enormous number of the ideas that were developed from particle physics, like field theory—quantum field theory has been applied to theoretical problems in condensed matter physics, and even in soft matter. Well, soft matter is not really a quantum problem, but statistical mechanics has been applied to that. Similarly, you can argue that ideas in condensed matter physics have also influenced high-energy physics a lot. For instance, the Higgs boson is an example, right? There was this theory of broken symmetry that was developed by Phil Anderson and others, and that idea led to Higgs thinking about that and coming up with the prediction of the Higgs boson. So I think it goes both ways. I wouldn't say soft matter physics or condensed matter physics is converging on particle physics or astrophysics, but a lot of the formalisms for dealing with the problems, the mathematical underpinnings, are strongly borrowed from each other.
Well, Sunil, it has been an absolute pleasure spending this time with you. I'm so glad we were able to connect. And it’s just remarkable to hear all of your insights and recollections over your career and your many collaborations. So, I'm so appreciative we got to do this, and I want to thank you so much for spending this time with you.
I should thank you, it was my pleasure.