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Photo courtesy of Mansour Shayegan
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Interview of Mansour Shayegan by David Zierler on August 10, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Interview with Mansour Shayegan, Professor of Electrical Engineering at Princeton. Shayegan recounts his family roots in Isfahan, and the political and social dynamics of growing up in Iran. He explains his decision to pursue an undergraduate education in the United States and the opportunities leading to his enrollment at MIT as an undergraduate. He describes his decision to stay at MIT for graduate school and his experiences in the electrical engineering program, where he worked with his advisor Millie Dresselhaus, during the Iranian Revolution. Shayegan describes Dresselhaus’s reputation as the “Queen of Graphite” and he describes the impact of her research on his dissertation on graphite intercalation. He discusses some of the commercial potential of his graduate research and emphasizes his primary interest in basic research and describes his postdoctoral work at the University of Maryland. He explains the origins of his interest in semiconductor physics in collaboration with Bob Park and Dennis Drew, and he describes the events leading to his faculty appointment at Princeton. Shayegan describes the work involved getting his lab and the MBE system set up, and he discusses the excellent culture of collaboration in both the physics and EE programs at Princeton. He explains recent advances in superconductivity research, and he reflects on the success he has enjoyed as a mentor to graduate students over the years. Shayegan expresses his pleasure in teaching quantum mechanics to undergraduates, and he explains his long-term interest in research on gallium arsenide. At the end of the interview, Shayegan reflects on his contributions to the field, its intellectual origins in the prediction of Bloch ferromagnetism, and the importance of securing the ongoing support from the National Science Foundation.
Okay, this is David Zierler, Oral Historian for the American Institute of Physics. It is August 10th, 2020. I'm so happy to be here with Professor Mansour Shayegan. Mansour, thank you so much for joining me today.
Thanks for having me.
To start, would you please tell me your title and institutional affiliation?
I guess that's Professor of Electrical Engineering, Princeton University.
Okay. Let's take it right back to the beginning. I always like to hear about where scientists come from and their family background. Let's start, first, with your parents. Tell me about your parents and where they are from.
My parents are from Iran. I was born and raised, in fact, in Iran, until I was seventeen. I came to the U.S. for college. The background, my father was a businessman, not so much into science, although he had some engineering background just learning onsite.
Where did your father grow up?
He was in Iran, too. All my ancestors are from Isfahan. Isfahan is the best city in Iran. Most beautiful. If you ever get a chance, you should go. We say [In Persian: Isfahan, Nesfeh Jahan], which means, "Isfahan is half of the world." So, if you don't go to Isfahan, you haven't seen half the world. My mother's side, she is in Persian literature, and my grandfather, her father, was a historian/scientist/philosopher. In those days, they were kind of everything. He's pretty famous, actually. His last name is Homaee, probably. That's how they would spell it. If you look here in the library at Princeton, they probably have at least twenty to thirty of his books and stuff. So, he's the one who is the scholar, or academic side. When I grew up, I was influenced by him. They [my grandparents] didn't live with us, but they would come during the summers and stay with us. He spent quite a bit of time with me. We would just sit there and chat.
Mansour, what were the considerations leading to you deciding to come to the United States to study?
Mainly, better opportunity to study. In Iran, in the seventies- even now there are similar problems, but it was particularly bad in mid-seventies. This is before the end of Shah. The universities were almost closed sixty to seventy percent of the time, except for medical school. The reason was the students would get together and would do some demonstrations against the Shah. He would send the guards in and they would beat them up, round everybody up, and close the university. That would be for three months, and then they would open again, and kind of the same thing. It would take like ten years to get a bachelor's degree. This was particularly bad with math, physics, and engineering, because I guess they couldn't stand the Shah. So, during my time in high school, many, many people came from Iran.
Were you from a well-to-do family? Did your family have the money to send you to the United States, or did you get a grant, or a fellowship, or a scholarship?
No, there were very few scholarships for undergraduates. My family paid for my undergraduate education. Of course, when I went to graduate school, then there was a standard stipend for graduate school. But undergraduates, they had to pay. There were very, very few scholarships. These days there are actually more. I know Princeton has some for foreign students, but in those days, it was very rare that you would get a scholarship at an undergraduate institution for a foreigner.
Did you know you were going to MIT before you came to America?
Good question. No. No. In fact, it's an interesting story. I ended up- it was the summer when I graduated, and I had made it to the electrical engineering school, physics, and also medical school [in Iran]. My father wanted me to go to medical school because he said, "Look, this [medical school in Iran] is stable." He wanted me to become a doctor, but I just didn't like it. So, in mid-summer, I told him I wanted to leave. My older brother was a student at Berkeley in engineering, so last minute he got me admission. In those days it was easier to get an admission, so within like a week he got me an admission to the U.S., but not from a top school. It was too late. You couldn't apply in the summer. I ended up in a school in California, University of San Francisco. Not the medical school. This is called USF, University of San Francisco. It's a Jesuit school. Business and nursing was their main field.
Anyhow, I went there, and I was even a week or two late because of the delays. It was very hard at the beginning because my English wasn't so good. I kind of dropped any course that I could drop, and only took math and chemistry. Things that I knew, and you didn't need to know much English. It worked fine. The professors knew. The math professor, for example, knew that I am there because I couldn't get somewhere else quickly. I told him that I wanted to leave. So, after a year, I left. They [the USF professors] were very helpful. They wrote very good recommendations. Then, I went to MIT as a transfer student. That wasn't so easy in those days, even now, because they take very few transfer students. But it worked out. I went there as a sophomore, and then I lost some credits, but eventually I did graduate in three years. So, it worked well. That was my father's thing that if I didn't go to medical school, I would have to go to MIT. This was his dream, I guess, and since my brother had gone to Berkeley, MIT was the other one that he knew about, and he wanted me to go there.
In 1978 and 1979 as the revolution was getting under way, were you concerned for your family? Were you concerned about what might happen to them while you were an undergraduate?
Yes. In fact, quite a bit. First, the revolution you're talking about the [President Carter] resolution, that all Iranian students should leave?
Right, so that happened when I was in graduate school. The hostages were taken in late '79, and I got my bachelor's degree in June of '79. I stayed on at MIT to go to graduate school, so I was in first year of graduate school. Then, the hostage thing came, and in summer of '80, when I was after the first year, that's when the resolution came. It was harsh, because the initial order was that the Iranian students had to leave, essentially, within two or three months. It was not immediate, but very soon we had to leave. In fact, I applied to schools in Germany and Belgium, and I had admission to Belgium. My advisor, Millie Dresselhaus, you may know of her, had the connection with Belgium guys.
So, I was about to go, but then MIT and Harvard, and other universities, sent a delegation to Washington, and convinced Jimmy Carter that this is not a good thing to do. Essentially, they said, "Don't make Iranian students your enemies. Don't kick them out. These are your friends." So, what the new resolution was- and I still remember, I got a telegram from Millie, because I was out of town from MIT. It said, "They said you could stay in the U.S. until your final degree." So, since my final degree was a PhD, that meant I could stay for another three years, because I was in the second year of my studies. Then, once the hostages were released, and the [U.S.] president changed, and so on, everything changed. There were no restrictions anymore. But it did affect many students. Like my older brother. He was about to get kicked out, so he had another route. He married someone, and then because of that he could stay. They were going to get married anyhow. So, yeah, many students were affected by this, and it was not nice.
Did you ever feel that you had to hide your Iranian identity during those years in the United States? Did you ever feel uncomfortable that this was not something that you wanted to advertise about yourself?
I think it's a little mixed. To be honest, because of my friends and my professors, no. I never felt that I should. They all knew who I am, and it was fine. I would say, out in the streets, I wouldn't advertise it. I remember well, this fellow named Gene Chamblerlain was the head of the foreign students' office at MIT. In fact, he had gotten to know my father and me when I was transferring. So, we knew each other, and I remember I went to his office for help. This was when the order was that you have to leave. I told him, "Can you help us? Is there something that you could do?" There were ninety Iranian students at MIT that this affected. He showed me a picture of the newspaper. You probably don't know this, but do you remember there was a failed mission that the U.S. sent? It was a disaster. The helicopters burned, and American soldiers burned. So, he showed me a picture of the soldiers' burned bones, and he said, "How can I defend you guys? This is the situation. I can't help you." But the professors were different. They really said, again, we're part of the community. Knowing that, then I wasn't afraid. I felt if there is any place I would be in the U.S., it's in school and at MIT. So, I never felt- but this kind of feeling, by the way, continues even now. The relations with Iran have never been good. Again, I don't want to say I keep a low profile, but it's best not to get into any political discussions.
At MIT, did you know you wanted to pursue the degree in electrical engineering right away, or did that come later on?
Actually, it came a little later. When I transferred, I started in physics, in the physics department. But then what happened is I was doing some independent projects as a sophomore, and it wasn't really the fault of my mentors, the professors who were mentoring me. I just didn't know a lot, so I was very bored. I decided physics is boring, even though I loved it. I just felt, my goodness, I can't do anything. So, I switched to electrical engineering. So, all my degrees are in electrical engineering, but I still love physics, so I just took physics classes, and quantum mechanics, and whatever I needed to learn. I was never officially a physics major except for one semester. It's a strange world. I have so many students who are in EE (Electrical Engineering), but they do more physics-y stuff. There are physics students who do more EE. So, it's very mixed, especially now.
What did you realize during undergraduate that you are most skilled at, and what you would want to focus on for graduate school?
When, you said?
Yeah, when during your undergraduate did you realize this is what you're really good at, this is what you're interested in, this is what you would want to focus on as a graduate student?
I would say probably from the beginning. The reason is when you're a foreign student, and you're good at math- at MIT, I'm in my background. I was very good at math and physics, and so on. My English was okay, but my father would always tell me, "You'd never be a good lawyer in the U.S." He encouraged me not to go back. He said, "Don't come back, just stay." So, essentially, the options were either engineering, or physics, you know, some technical field. Of course, in those fields, I felt it's best to get the highest grade that you can. So, my grades were good, and my mentors, Millie Dresselhaus, and others, were very encouraging. I did these undergraduate research programs in my junior and senior year. Those are much nicer. They were telling me, "There's no question. You should stay and do a PhD and stay at MIT because we're the best." So, I'm a pure product of MIT except for that first year. I didn't go elsewhere. It worked well because I finished my PhD in four years, which is pretty good. Millie Dresselhaus essentially said, "Stay, and you could do a quick PhD because you know the lab and you know the field." So, that worked well.
When you committed to staying on at MIT, did that also mean in your mind that you were committed to building a life for yourself in the United States, or did you think you would take that PhD and go back to Iran?
I think, in those days, it was very hard to go back to Iran. These are post-hostage days, where it's like two or three years after the hostages were taken and released. The government in Iran was going downhill. At the beginning, there was hope that these clergy won't be in charge, that there will be some democracy. For one year, it was reasonable, actually. But then there was really a void. There was no one except these clergy who had any say, and they took over. I don't want to get into the politics, but essentially, under that kind of a government, it's very hard to live there. In fact, my mom was a professor at the university in Iran. She came back and forth, but after a couple of years, she left forever. She said, "It's just too hard to work here, for women, especially." So, she came out, and she stayed near MIT. So, I think, given the political situation, it never occurred to me to go back. It was clear that the future is better in the U.S.
Mansour, how did you develop your dissertation topic at MIT?
As I said, since I was an undergraduate there, I had to do a senior thesis. I did it with Millie Dresselhaus, and that's when she also told me, "Look, why don't you stay? You could get a quick PhD." So, essentially, since my senior year, I knew I wanted to stay. I applied to other schools, but I didn't go. So, I would say from my senior year- it was this graphite intercalation compounds, which was a big deal in those days. So, I just stayed and did it.
Was this research related to what Dresselhaus was doing?
Absolutely, yes. Millie and Gene Dresselhaus, [as a] couple, were in this field. They were probably the biggest contributors. In those days, Millie had a big group, in fact, with maybe thirty members. Gene was not a professor, but he helped all the time. He was a theorist, officially hired at the Lincoln Labs, but he would get some salary through grants and stuff. So, essentially, he would help us. Not so much in the lab, but with the theory part. Those two were my mentors. The big field was graphite intercalation. They [Millie and Gene] did that for many years until high -Tc superconductivity came. They switched for a while there, and then much later, of course, the graphene. Millie got involved in graphene, too. So, she is "Mrs. Graphite." She was the Queen of Graphene, or what did they call her? Queen of Graphite? I think I read that somewhere. Shortly before she died, there were some advertisements put out by GE, and it said that she's “Queen of Carbon,” that's it, Queen of Carbon. She was a wonderful person, by the way.
What were some of the bigger research questions in the field of graphite intercalation that your work as a graduate student was responsive to?
It was, I would say, not near the end, but it was mature already. Many things had been done, so I would say one was intercalating magnetic layers between the carbon layers, like cobalt chloride, so that the final system would have some interesting magnetic properties. There was some, like if you put mercury, it became superconducting. There were a few things. In those days, there was no big MBE program, Molecular Beam Epitaxy. So, to grow layered structures, this was a technique to do it in a very cheap way. You just stick a piece of graphite in a furnace, put mercury or whatever you want, and then put it in the furnace for a week at two different temperatures. You would keep the two ends of the furnace at different temperatures, and then you would come up with the graphite intercalation compounds. It was a poor-man way of making super lattices. It was a fantastic field, but I would say in '86, '87, I still remember this- I graduated in '83 from MIT, and then in '84 or '85, there were still many, many sessions at the March meeting on graphite intercalation. Then, '86 came the high-Tc. In '87, if you went to the sessions, maybe one out of ten people were still working on graphite intercalation. Everybody had switched to high-Tc, or something else that was not graphite intercalation. And then, of course, some serious people came back. That was near the tail end of it.
Why did high-Tc have this dramatic effect on graphite intercalation?
I think the reason was it was very exciting. It was new, and it was very promising that maybe it would make room temperature superconductors. Again, the graphite intercalation field had matured, so there weren't so many easy things left to do. I think it's natural. This happens. Like, when graphene came in the mid 2000s, many of the old graphite intercalation and fullerene switched to graphene, because it was new and exciting, and they had some background in it. So, they switched. Millie was back in- I believe she has many papers in graphene. So, I think it's a question of when something is not as exciting as it used to be, or it's pretty mature, and the new thing comes, then people switch. The problem is too many people switch. As you know, they just jump on the bandwagon, and it takes a few years for the ones who just jumped from one train to the other train to go off their own ways, and some serious people stay in the field and keep working in it. In my case, I have never had so much interest in jumping like when graphene came. Maybe I should have, because I was very suited. It was what I used to do for my PhD.
Mansour, for yourself, and for the Department of Electrical Engineering generally, I'm curious if you can talk about the approach to just understanding the science versus being interested in commercial applications of the research as a motivator for working on particular projects.
Yes. I would say, personally, my interest is ninety-nine percent in the fundamentals, and just the curiosity of why things happen the way they do, or whether new many-body phases occur, and so on. These seldom have application. If there is an application, usually it's very far-fetched, like topological quantum computing. Sometimes we see [relevant effects], or we put it in proposals, and it's a great motivation. No problem. But my own interests, and I would say ninety-five percent of my funding, even though I'm in electrical engineering, is for fundamental stuff. It's mainly NSF, DOE, through their basic science and engineering programs. From the NSF, we sometimes get grants, which are application oriented. But I would say, [the funding is for] what you call a prototype, proof of principal, to show that something could work. But we are not interested in making a device to be faster or better.
Would you say that your approach in focusing on the fundamentals is representative of the department as a whole at MIT? Is that how most people operated?
No, no, no. Not at all. MIT was and is huge. The electrical engineering in those days was, I think, 500 students, which is huge. It was like maybe half of the class. Of course, they had many professors, and it's combined. I think even now, it's electrical engineering and computer science. The way they do this is they break it into many branches. So, in those days, there's computer science. Then there's another one in signals, and one in, I don't know, electronic devices. So, there was a branch which was solid state materials and devices, and that is where Millie's research was. So, I think even though it was in electrical engineering, [it was] kind of the same as what I'm doing here.
In electrical engineering, there was physics, but maybe it was ten to fifteen percent of the MIT EE, in those days. I believe it's roughly the same right now. Maybe even less. All the solid-state physicists I know now at MIT are all either [in] physics or materials. Not many of them are [in] EE. There is no applied physics department at MIT, so that's why- same here, by the way. Very similar. We don't have an applied physics department, but in our department, out of twenty-four [professors], maybe a handful actually do physics-y stuff. I'm probably the one who is most fundamental among the experimentalists. The other ones do the physics part but it's more motivated by some device, and then the funding is more on the application.
So, Mansour, for your research, what theoretical work is most important and relevant to you?
What we do is we call it many-body physics; electron-electron interaction. This stuff is not so intuitive. For me, by now, some of it has become intuitive. Not that I understand it all, but at least I can get a feeling and when a theorist, or when I read a paper, I kind of know what they have in mind. So, the theorists, I would say, if I could mention some names, like Duncan Haldane in physics, or David Huse in physics, they are the theorists I talk to most. We have a theorist here, Ravin Bhatt, who is in fact like me. He is in fundamental physics, but he is in EE. So, we talk. So, what the theorists provide, I would say, some of them, like Steve [Girvin], he gets really involved with experimentalists, and they have joint papers. Here, we don't have many who are- I don't want to say interested, but it's not their main strength. Like, Duncan Haldane, if you talk to him. It's hard to communicate. He's brilliant, but you know. We have a couple of papers- maybe not even a couple. I don't remember. It's harder. With Allan MacDonald or Jainendra Jain, or Roland Winkler, we have had papers. It would be wonderful if we had someone like Steve who we could talk to and speak our language. Unfortunately, we are small, and the field is so that we don't have it.
Anyhow, back to what theory I like best. I like it if they propose something that we could do. I hate it when they say this, this, this, and then you say, "Well, how can I test this?" "We don't know, or the prediction can't be discriminated." The other thing is sometimes they explain phenomena, so that's nice. And sometimes, they predict, and we can go and see it, but I wish there were more of it. We do have a paper coming out in Nature Physics. This is a good example [of our work] with Jaindendra Jain. I don't know if you know him. He's at Penn State, a theorist. He's very nice. He talks experimentalist’s language. So, he did the theory part, and we did the experiment. It's a nice, combined work. That's coming out soon.
Given your interest in the fundamentals, you never thought about entering industry after you defended your dissertation. You knew you wanted to stay in academia.
Good question. Again, my parents' role. I knew that I wanted to go to an academic’s job, but my father was appalled that I'm turning down an offer by Eastman Kodak in 1983. It was like, I don't know, $50,000, and I'm taking a post doc position for $20,000 at the University of Maryland, which is not even a fancy school. But I just felt, no, I want to stay in academia. I think it has paid off. I have never felt that I wish I were at Eastman Kodak. Bell Labs and IBM Research would have been more comfortable for some time, but the past twenty years, no.
What about your research would have been attractive to a company like Eastman Kodak?
I asked my advisors for suggestions, and I think they came to [MIT to] recruit, I'm pretty sure. I met them, and I talked to them. The project was very nice. They wanted to get into optical- they used to be film. They still do some film; that's Kodak. But they wanted to get into digital and optical, and this was a nice time to go. So, the project sounded interesting, but it was applied. It was for this purpose, and I preferred to do more fundamental research.
What were you doing at Maryland? What were some of your research projects?
Those were actually in the physics department, and they were, I would say standard physics/chemistry. It was chemisorption of oxygen on nickel surfaces when you cool the surface, and so on. The long story there, again, is Millie. I was in her office going over my thesis, and the telephone rang, and Bob Park, you may know Bob Park. He just passed away recently. They knew each other. They were part of the officers at APS. At some point, Millie said, "I've got to go. My student is waiting here to go over his thesis." And then Millie says, "Oh, you're looking for someone? Here, talk to him." And she handed me the phone. This was spring of '83, the year that I was graduating. Bob Park talked to me for five minutes, and said, "That sounds good. What can I do to get you to come to Maryland?" And I said, "Get me a green card." He said, "Are you serious?" And I said, "Yes." Because even now, as you know, I said, "I'm a foreign student and I'd like to get a green card to stay here." He said, "No problem. I know the right people at the university. You don't even need a lawyer." Indeed, within six months, I got my green card, which was kind of a miracle. So, that's how I ended up at Maryland. I had offers from Harvard and Princeton, but they weren't willing, or they didn't know how to get a green card. With the green card, you have to have a permanent job. So, at Maryland, they kind of made it permanent. As long as there was funding, I could stay there.
That sounds like a pretty smart way for Maryland to compete with Harvard and Princeton.
Yes, exactly. And Bob Park was a wonderful man. I enjoyed it. I really liked Maryland, because it was low-key. It wasn't as high pressure as MIT or Princeton. I really liked it. It was nice.
Were there any significant differences working in a physics department as opposed to an EE department at Maryland?
No, because I was not teaching. I was just doing research, so I don't think so. I met many physics students and professors. I have some engineering friends, mainly through playing soccer on the side. There, it didn't make much difference. At Princeton, there is a big difference. In physics, they teach big classes. You know, the freshman physics, and so on. So, it's a different teaching schedule. In EE here, my biggest class ever has been maybe thirty students. I take it back. I taught some circuits thirty year ago, and that was maybe fifty. But I would say average is fifteen students, which is wonderful. In fact, I remember this very well: when I was getting the Princeton offer, I asked Millie for advice. She told me, "Don't hesitate. This is a dream job for anyone interested in academia, because there are good students, and small classes always. It's wonderful. Just take it." And she was right.
Did you first get interested in semiconductor physics at Maryland, or did you bring this with you from MIT?
It happened at Maryland. What happened is I was doing my surface science experiments, but these experiments take time. You close the chamber and bake it for like a week to get the pressures lowered. It's a vacuum system. I was kind of bored, so I was trying to find other things to do. There's a fellow, Dennis Drew. I don't know if you know him. He's a physicist. He just retired a few years ago, and he lives here now, in Princeton. Very nice man. Anyway, he was there, and I started to play squash with him. We both played squash. And I was kind of complaining to him that I wished there was something else I could do while I'm waiting for this thing to cook for a week. We started to chat, and we thought about these experiments on mercury cadmium telluride, and indium antimonide, which are these narrow-gapped semiconductors. There were [claims of] Wigner crystals, and so on.
So anyhow, I got interested, and Dennis Drew- the two of us would go back to the magnet lab where I did most of my PhD and did the high field experiments. Those days, the magnet lab was at MIT. So, I got to know Dennis, and this is how I started to know semiconductors. Then, the next thing that I feel was my best luck was that at Princeton, Dan Tsui, and other senior people- Dan Tsui was in EE. He was never in physics. He knew about my semiconductor work, because we had run into each other at the magnet lab. I talked to him, and he also knew about my surface science work. That was what I was doing at Maryland. The combination of these, he thought, was great for somebody to come and do molecular beam epitaxy, which is also high vacuum stuff. So, that's how I got the job offer. He said, "Would you like to come and set up an MBE system?" I didn't have direct experience in MBE, but I knew the ultra-high vacuum part, and I knew the semiconductor part. So, this worked really well when I came to Princeton.
So, you didn't even really go on the job market. This all just came together for you at the right time.
No, there was a little bit of a timing issue. First, I had an offer from Maryland in the EE department. But they were interested in physics-y stuff. They wanted me to stay, and they said, "Why don't you stay?" I had an offer from them, and I had accepted verbally, but nothing signed. The letter was not coming, and it takes time because it's a state school. And then, again, I ran into Dan [Tsui] at the magnet lab, and he heard. He said, "I hear you're looking. Why don't you come to Princeton to talk?" I said, "Sure," and I came quickly. Then they offered me right away, and I said, "But Dan, I have this offer [from Maryland]." He said, "Have you signed anything?" I said, "No." And he said, "Well, then you're not bound to anything because they haven't given you an offer." So, I talked to Dennis Drew and Bob Park who were my mentors at Maryland, and I said, "What should I do?" And they both looked at me, even though they wanted me to stay at Maryland. They said, "Are you a fool? Go! Princeton, if they're offering you a good job, don't hesitate." So, that was it. So, I was looking already, but this kind of came as good fortune that Dan Tsui knew that I'm looking.
As part of the offer, what kind of support did Princeton offer in terms of helping you get a lab up and running?
Not much. The problem was in those days, including Dan when he came, they gave him very little. He came in '82 or '83, and they gave him very little. Those days, universities weren't used to these big start-up funds. There wasn't much money. They gave me, I think, around $150,000, but the MBE, even in those days, cost about $1 million. So, there was no way I could buy a nice, new MBE system to run it. But again, through a series of fortunate coincidences, I found out that Varian, that made the vacuum chambers, the MBE, they had the tax incentive that if you could get fifty percent of the money, they would donate the other fifty percent, because they could take it off their taxes. So, essentially, I needed $500,000.
Then, again, by pure accident, New Jersey Commission on Science and Technology had a program that if a company donates so much money, they would match it. It was just like a miracle. New Jersey Commission didn't have enough money to match the half million, but they had around $300,000. So, all together, all of a sudden, I managed to get a new MBE worth $1 million with $150,000, which was my startup money. It was amazing, but it worked well. If I didn't get that system, I would have gone nowhere. I was planning to build one, but it would have taken forever to build one, and I didn't have any experience. I had never done MBE, so it was tough.
Once you were able to get the MBE system up and running, what were some of the major research questions that you wanted to explore?
Right. MBE is material crystal growth, right? I always wanted to do the physics too, and it turns out, when I was finishing my post doc, when I had the offer from Maryland, I also had an offer from IBM to go and do MBE, because they were also interested in my interest in crystal growth and semiconductors. But Leo Esaki was there, and essentially, they told me, "Whatever Leo says, you have to do. If he tells you to grow this, do it." I didn't like it. I wanted to grow something that we could study ourselves and do the physics. For me, it was very important that we do the physics in my lab ourselves. So, that worked well, because Dan Tsui here was also very interested in the physics and has always been. So, it was a good collaboration. Many of our first papers in my group were done in collaboration with Dan. Part of it was because I didn't have any low-temperature equipment. I got money for the MBE, but I didn't have a dilution fridge to do low-temperature measurements. So, I relied on his lab, and then slowly I managed to get enough money so we could have our own fridge, and for twenty-five years, I was doing both growth and measurements. It was wonderful. It was tough because not many people do both. You either focus on the growth or the physics measurements. But this was great because we could do both, but you can see my white hair, and no hair! Much of this comes from those days. Very stressful.
So, just to continue on that, about ten years ago, Loren Pfeiffer, who was at Bell Labs at the time, was a competitor. We used to compete in high mobility. Not in a bad way; he's wonderful. He always shared information, and we shared information. We knew each other very well. But Bell Labs was very difficult to work at starting fifteen to twenty years ago. At that time, he had interest in leaving Bell Labs, so he came to Princeton. He brought his MBE machine, and the plan was that we build a new MBE machine to break all records. Indeed, it has worked well. It took eleven years, but just these last few months, we have a world record. It's mostly to his credit. Now that he's here, I do less of the MBE. I know all the details, and we chat all the time, but I don't have to do it in my group. We can focus on the physics.
When you say that you've broken a record with MBE, what does that mean, exactly? How do you quantify that?
The main thing that we do are these modulation doped structures. Imagine, it's a layer of gallium arsenide, sandwiched between aluminum gallium arsenide, which is a larger band gap material. It forms a quantum well. Essentially, the energy is lower for the electrons to go into the gallium arsenide layer, that plane. The great advantage of this is when the electrons come from far away, they leave their parents, the donors if you wish, behind in the barrier, and they jump into the quantum well. Because of this, they are far from the ionized impurities, so in this plane, they can go very far without getting scattered, of the order of a tenth of millimeter. It's amazing, at low temperatures. The mean free path for these electrons in the plane is very long.
Another thing that happens is, because they [the electrons in the quantum well] are not bound to the donors and don’t interact with the donors, they interact along themselves. The electrons are charged, so they push each other and form these fancy states that we study. For example, one of them is this Wigner crystal. I'm saying it as an example because it's very easy to see. Imagine a bunch of charged particles. They push each other, they repel each other. So, it turns out the stable form, phase if you wish, is a triangular or hexagonal array. Imagine a graphene sheet, but in the center of the open hexagon you have another electron, so it’s triangular. They [electrons] are all there in a patterned triangular way, because if they move off from their position, they get pushed too much by the neighbors. This is called a Wigner crystal, predicted by Wigner in 1934. It's one of the holy grails that- actually, we can see it in some samples.
Anyhow, the great thing about these systems is [that] you separate the electrons from the donors, and they go very far without getting scattered. A measure of how far they go is this electron mobility. Mobility is defined as how fast the electron goes for a given electric field. In other words, if you put a force on it [the electron], how fast does it go? The units are centimeters squared per volt second, and in those units, the world record was thirty-six million until a few months ago. Now, with these new samples, we have like forty-four million, and maybe even forty-nine million. That's just a number. It tells you these are purer than any sample before. These electrons can go farther and faster than ever before. But that's not that exciting to me. More exciting is what states can you see in them? Back to this electron-electron interaction. There are already some interesting signs that these samples are going to show new stuff. There are new factional quantum Hall states. There are new phases that will show. So, in this field, over the past thirty or forty years, every time there is an improvement in sample quality, it's followed by some interesting new physics, new phases. In that sense, the mobility is the world record, and the physics, hopefully, would follow.
What have been some of the major discoveries in these past twenty-five years that you've been involved with in these fields?
One of the early ones was the Wigner crystal at the high magnetic fields. The samples, even then, were good enough that you could see some glimpses. In the samples that we grew in the late eighties, early nineties, we have some papers. Wigner crystal is one. Another one is bi-layer systems. Imagine, you make two of these high-quality layers next to each other so that you have an additional degree of freedom, or an additional degree of interaction, if you wish. This additional degree leads to new states, like even-denominator fractional quantum Hall states. We are the first to see the even-denominator state in the lowest Landau level, in this bi-layer systems. So, that was exciting. There are many other things. Electrons in parabolic wells. In those, you can make thick electron systems that still interact. whole system through the holes. We had the world record and exciting physics in the Wigner crystal stuff. It has continued in that way, and our interests are essentially in these collective states of these systems.
Where is the field of superconductivity now, relative to when you first got involved?
I didn't. I was never involved in superconductivity. These gallium arsenide samples, the ones that we work on, none of them show superconductivity, so I was never involved in high-Tc or low-Tc.
But you're saying you would have been involved had they shown superconductivity.
If they showed, but to the best I know, they're not supposed to. The conditions are not there. The ones that are showing superconductivity, these are the bi-layer graphene systems. There, the magic is that you can put a layer of graphene, and then you put another layer slightly rotated, by about one degree rotated. This makes the system very narrow band. The band width becomes very small. That helps the interaction, and then you do get superconductivity. This was discovered by Pablo Jarillo-Herrero. He is at MIT. But we can't do that with gallium arsenide, because when you grow these with MBE, there is no way to control the next layer to go one degree rotated. They just go where they belong. The beauty of it is that it's a single crystal. The disadvantage is you can't make these twisted angles. You have a twisted angle layer. So, I think the prospects of superconductivity in gallium arsenide and related structures is low. They're having predictions here and there, but nobody has really seen much. So, that's not the goal.
Can you talk a bit about how your research moves forward many-body physics in general?
Move forward, you mean as things get discovered? Yeah, I think sometimes theorists predict some new state that could happen in certain structures, and we go after [it], and it sometimes it happens. An example is the stripe phases. That's another phase of these two-dimensional systems. Electrons form like a zebra, high-density, low-density. That's an example of where the theorists were ahead of us. They predicted this, and then a few years later, people could see them in the best quality sample. Often, it's the other way. We're looking for something, and then we see something which is a complete surprise that nobody expected, including the theorists. To me, that's the most exciting, because that's a real discovery, if you wish. And then, often, or sometimes, after a few years, the theorists catch up and explain it.
So, I would say it's both ways. In my lab, I tell my students to look for new things. They each have a project to study something that we know should work, but they have to stay alert and look for anomalies, for anything that is not as expected. By the way, I say that in my proposals, too. When I write a proposal, at the end, I have this concluding paragraph that says, "So, I have described now these ten projects that we plan to do, but I hope we won't be doing these projects only. I hope that we will run into something unexpected, and then we would follow it." To be honest, the reviewers like it. They agree that's the best thing to do. It's guided both ways. An example, not quite in my field but related, is the superconductivity in these twisted layers. That was predicted a few years ago- not quite, but the structures were proposed by Allan MacDonald and his post doc, and then later it was seen. So, that was partly expected, but then a big surprise came that [there was] not only that phase, but there are other phases nearby. These are phases I like to see.
Mansour, obviously, your initial interest in exploring the fundamentals has remained the same. I'm curious, over the years, if there have been some industrial applications or possibilities that convinced you, maybe, to pursue a patent, or talk with companies. Have you ever come across any opportunities like that that you were interested in?
A couple of times. In fact, a couple of times we even tried to write a patent to file. The problem is that ninety-nine percent of what we do is at low-temperatures and high magnetic fields, and those are not that exciting for companies. They don't want a device that you need to cool. The exception is quantum computing, because at the moment, anything that you could do, if it works, it's great. Anyhow, that's the problem. The other problem is from the government, I have tried a couple of times to get the money for the application part, but to be honest, I would be lying to them if I said, "Oh, this is going to work for the military, or whatever."
But I'll give you a quick example. Some people from the Army Research Office, ARO, many years ago. We [had] made this extremely sensitive strain sensor, essentially a strain gauge. So, if you changed the strain by 1 part per million, you could see it in the resistance of the sample. This is amazing; better than anything you could imagine. I made a presentation, and they listened carefully. One of them said, "This sounds great. I would love to have one of these in every soldier's backpack. Would it fit?" I said, "You know, the device, absolutely yes, because it's a tiny little chip. But I don't think the cryostat and the magnet would fit in the soldier's backpack." So, that was the last of their interest. So, I would love to, but it's not so easy to find. Again, some agencies are interested. NSF, for example, is interested in a long-term devices approach, so we get some fudging from them, and we try.
Who have been some of your most successful graduate students over the years and what kind of research have they pursued since working with you?
One of them is Hari Manoharan. He is now a professor at Stanford. He completely switched fields, of course. He did a great PhD. He was one of my best students and wrote wonderful papers. But then he did a post doc at IBM, with a fellow named Don Eigler. You may have seen pictures. They move atoms on the surface. They wrote IBM- this was thirty years ago. So, this was a big deal. So, [Hari] worked with him and became very interested in this field, and now that's what his lab is set up, and he's doing well at Stanford. He’s pretty successful. He's a professor there, but the field is a little limited because there's not so much you can do with writing things and moving atoms around. But he is doing well.
Another one is a fellow, Emanuel Tutuc. He is at the University of Texas in Austin. He has a very nice program. He also went to IBM to do a post doc, and now he is doing quantum materials and 2-D materials, graphene and stuff. He got in early and is quite successful. One of my early students, who was in fact my second student, Mike Santos, he's a professor in Oklahoma. He's doing very well. And there are a few more, Yuen-Wu Suen, Jean Heremans, Javad Shabani, Medini Padmanabhan, Yang Liu. And in industry, there are many more, Jeng-Ping Lu, Stergios Papadakis, Etienne De Poortere, Yakov Shkolnikov, Babur Habib, Kamran Vakili, Oki Guanwan, Tayfun Gunawan, Doby Kamburov, M.A. Mueed, Hao Deng- I have many students at Intel and IBM.
So, as a mentor, Mansour, if your students have expressed interest, you certainly encourage them to pursue those interests in industry if that's the best place for them.
Absolutely. For some of them, it is indeed much better. I think most of them kind of know it. They come and when they start to look for a job, when we chat, it's clear that their interest is in industry. So, we don't even go through the post doc route. I think it's maybe two thirds have gone into industry, and one third into academia over the past many years. I don't have many students, by the way. I have, on the average, one student a year. My group is typically small, so I would say maybe thirty-five students, or so, that have graduated of that order. Fewer than Millie!
The students who have gone into industry, what commonalities do you see in terms of the kinds of work they've pursued coming out of your lab?
I think probably the best characterization is careful, because they do very meticulous and careful research. Not just taking data but analyzing it and writing it up. I feel many of them are going in that direction, initially, at least. Of course, after a few years, they may go in the management side to grow. But I think that's what I would say is the main theme. They go on some project which needs very careful measurements and deep physics, essentially. But some of them, no. Some of them are entrepreneurs. I have a student who set up his own company in digital tech some years ago. He sold it to Intel for a lot of money. He now switched to some other field. So, they become entrepreneurs. I have another one who became a patent lawyer. So, there are all kinds of them. The ones who stay in the technical part, I hope what I've taught them is to be very careful and do solid stuff. Don't do anything superficial.
Right. On the undergraduate side, looking back over the course of your career, what have been the most enjoyable courses for you to teach undergraduates? What do you like teaching the most?
Quantum mechanics. I teach a junior level course, but some sophomores take it too. This is quantum mechanics for engineers. The physics department has a whole sequence. This is a one-semester course that the juniors and seniors take in our department, and sometimes from mechanical engineering. So, it's around ten students a year. I love it because it's their first deep encounter with quantum mechanics. It's so exciting for them, and for me, that there is uncertainty, and Schrödinger's Cat. The way I teach it is the way I learned it at MIT in a similar course. I took quantum mechanics in EE at MIT. It wasn't a physics department course. David Adler used to teach it.
Anyhow, it's kind of intuitive. It's not deep into the equations and stuff. Of course, we do Schrödinger equation in more depth. I love it because I can just see that they're all excited. I even tell them, "You can impress your humanities friends with the question like, is the sun there when you don't look at it? Is the moon moving when you don't know anything about it?" Things like this. That, to me, is the most amazing. Solid state physics is another course I teach to undergraduates and graduates. It's interesting too, but it's more dry. It assumes they know quantum mechanics. Anyhow, quantum mechanics is it. I love it. I never get tired of it.
Mansour, I wonder if you can talk a little bit about the growth of computational power over the decades, and how this has been relevant for your research.
Since we don't do any deep level theory, we don't use computation in that sense. It's more data taking and analysis, which requires some computation of the data. I would say it is amazing how far it has come. In Millie's group with Gene Dresselhaus, they were at the forefront of using computers. I remember we got a DEC computer, one of the very early Digital Electronics Computers. It was like $30,000 and was state of the art. Of course, it did much less than a calculator would do, literally, right now. But this was the thing that would take data and analyze it. Before then, I would have to do it on paper. It was a pain. I could take only like 500 points at a time. It was amazing. Now, they can do that, I don't know, 1000 times faster. So, that has changed things. Sometimes, not necessarily for the better.
Again, when you're taking data and thinking and analyzing it -- in the old days, we recorded a trace, we would think about it. Just as the trace is being drawn on those plotters- you [probably] never dealt with those, but it was a real pen drawing the thing, and it gave you time to think and analyze it. These days, of course, they just push the button and the data comes, and they have like twenty traces and they haven't even analyzed them or understood them, and then they go on to the next one. As I said, I'd really like them to see the details and figure out what's going on. Sometimes, they don't know it until a few days after they have warmed up the sample. They come and show something to me, and I say, "Oh, this looks fantastic. Can we take more data?" And they say, "No, the sample is already warm." Anyhow, back to this question. It's amazing how much you can do. It accelerates taking data, eventually writing papers, publishing stuff. But it is not as easy to think as you're taking it, when you do it so fast.
Mansour, just to bring the narrative up to the present day, what kind of projects have you been working on in recent years?
The recent ones, one of them, which has always been there, but the improvements have come recently, is this high mobility stuff in gallium arsenide. Another one which we have done quite a bit the past few years is the following: normally you trap these electrons in gallium arsenide, but it turns out you could also trap them in an aluminum arsenide layer. It's a different semiconductor, and its properties are very different. There's multi-valley, different conduction band valleys. The problem is that aluminum arsenide can catch impurities very easily: water or oxygen. So, as you're growing this, you need a really good MBE system. So, because this new MBE, now, is so good, those samples are much, much better than what we had, say, ten years ago. The gallium arsenide, I told you, we made an improvement of maybe thirty percent in mobility. These electrons in aluminum arsenide are literally ten times better. The mobility is ten times higher. There is a lot to do in the system, because it's essentially like a brand-new system. It's different from gallium arsenide, so we can study them. I have like two or three students right now, half of my group, focusing on this aluminum arsenide. Other stuff is these bi-layer systems we're continuing, but I would say the most exciting is the aluminum arsenide, and overall, these new high-mobility samples.
Now that we've gotten up to the present day, for the last part of our talk, I want to ask you a broadly retrospective question about your career in research, and then one that's more future facing. Because you've always been so dedicated to the fundamentals and the discovery, I wonder if you could talk broadly about not just your research, but the field in general. What are some of the things that were really not well understood from the time you were an undergraduate, and what advance have been made, and specifically, how have you contributed to those advances for things that are really pretty well understood today.
The phenomena which were predicted but not seen, those, slowly, they're being seen more and more clearly. There are more experiments that affirm them, if you wish, or we learn more. Let me give you one example. You'll see what I mean. This Wigner crystal business has been going on from 1930’s. It was only the past, I would say, forty years that there were believable glimpses, that there is something with this crystal formation. An experiment I'm very proud of that we did about three or four years ago, is we made a bi-layer system, so there are two layers. One of them had very low density. When you go to high fields, this layer could form a Wigner crystal. The other layer, right next to it, 100 or 200 angstroms away, that has very high density, so it turns out it has these composite fermions. Essentially, imagine electrons that could go around the orbits, around circles, if they see the potential of the other layer. So, the periodic potential of the Wiener crystal layer, these guys could detect. You could see whether they were going around one bump, or three bumps when the orbit is bigger. You follow what I mean? I don't know if this is so clear. Imagine a triangular network. Say the period is one centimeter. Imagine another particle could go around one of these circles, or there of them, or seven of them. In a triangular lattice, these are the integer number of dots that you could go around. Anyhow, long story short, we could see, really, that there is a Wigner crystal lattice that these go around one or three or seven. We could even measure the lattice constant of the Wigner crystal. I felt this is great, and Phys. Rev. Letters actually had a commentary about it that finally you can see Wigner crystals directly. So, this is an example. The phenomena is not new, but finally there is solid evidence. I don't want to claim that I'm the only one who could do this stuff.
The other one is these unexpected phases. There is no end. On the one hand, you could say, so what? What if there is another new phase? But curiosity. If your main interest is what happens if I do this, or what does nature want to do when you put it under this condition? To me, that's always exciting. If it has an application, it's even more exciting. But if it doesn't, it doesn't. Another example is- we are just writing a couple of papers, and another phenomenon- Felix Bloch, you might have heard of Bloch. In 1929, he predicted this Bloch ferromagnetism, which says if you have a bunch of electrons, when they interact, before they form this Wigner crystal, they align all their spins. They start as a paramagnet with spins it up and down, but as you lower the density, all of a sudden, they should form a ferromagnet. This, nobody has really seen. There were claims, but I can tell you why those are wrong. So, finally, we see them. It's amazing. We have, I feel, the most clear, unambiguous data that shows that this does happen as you make the system more and more dilute. We have one paper coming out that's in Nature Physics, and we have two other manuscripts that we're about to send out. To me, that's amazing. That's great, that somebody predicted this so long ago, and it was always elusive. And finally, we can see it.
What explains that? From 1929 to now, is it technology? Is it just the hard work in the lab, day in and day out? What took almost a century for this to be proved, experimentally?
Quality. It's the quality of the sample. What happens is, imagine the Wigner crystal. If there are no impurities, nobody pulling the electrons in different directions, then they do interact, and they form this ordered array. No sample is perfect, [however]. There are always impurities. So, the reason these phenomena show more clearly, or show at all, is because the impurities are very few. That's how we get the better mobility. Essentially, we get purer and purer material, and that's how they show [new phenomena]. I would say it's sheer force of making purer material. In MBE it's combination of very high vacuum, and this recent success [also involves] making the source material very pure. This is gallium, aluminum, the stuff that you evaporate and grow the layers. They are so pure. Essentially, it's one part per roughly 1010 to 1011 pure. That means only one out of 1010 to 1011 atoms is an unwanted impurity. Can you imagine? And we are growing this [material] layer by layer. Each layer takes about a second, so in one second, when you're growing this layer, only one part per 1010 to 1011 impurities come. You can imagine the vacuum has to be really good, and the material has to be very clean. This takes years to do. For maybe thirteen or fourteen years, the world record was just stuck because nobody could do better. Now, one can do better, and now we see this Bloch ferromagnetism, and so on. So, crystals. In these cases, the quality of the samples matters.
Same with graphene, by the way. Initially graphene was dirty, and they couldn't see much. But [during the] past ten years, they get cleaner and cleaner, and they can see fractional quantum Hall effects, and now superconductivity. All of these require clean sample. So, materials. I should tell you, it's really unfortunate that in the U.S. it is hard to get funding for research on materials. You may have heard this from others. But right now, I was talking to the NSF officers. I was telling them about how wonderful these new samples are. I was telling them I like to write my own proposal for the physics. That's what I always do, and the materials is on the side. I was telling them, "Is there any way we can get funding for Loren Pfeiffer and the MBE effort?" The guy says, "No, no, no. Be very careful. If you send a proposal that says you want to improve the quality, that won't cut it."
Yeah. It's not like that in other parts of the world. In Japan and Europe, they have better materials programs. They fund their materials efforts.
You're saying that this has changed over the course of your career, that NSF and other funding agencies were much less restrictive about funding basic research twenty or thirty years ago.
Well, I think the DMR, the Division of Materials Research, which is where I get my funding from the NSF, or the DOE, they have always been interested in the fundamentals, but the part I was complaining about is they are very interested in the physics, but they are not so keen on funding the materials part, like the MBE. So, if you ask for just one grant, you know, $200,000 a year to improve the MBE growth, the vacuum, to get these better samples, they're not that interested. I believe the NSF, even its Division of Materials Research, consider MBE too mature.
What they would tell you is to write it in terms of physics, that I want to do this physics, and this physics, and then okay, we could use some of the money to grow some of the materials, which is what I've been doing all these years. I put the physics first, but it's limited. Somebody like Loren, who is doing the MBE, the only source of funding is through the Moore Foundation. It's very limited. The reason is the NSF, even though it's Division of Materials Research, they consider MBE too mature. They're more interested in materials which are very unknown, or much less known. To perfect something, essentially, they're interested in perfection. They're interested in new plastics, or I don't know. It's a difficult situation, but we have lived with it, and we can go on.
For my last question, you've touched on it a little bit. In a perfect world where you didn't have these funding constraints, and thinking about your ongoing interest in the fundamentals and discovery, what are some areas of research in your field that are really still poorly understood, and how might you devote your time and energy and resources toward those areas that there is still fundamental knowledge to be gained?
I must confess that my interests in my field are rather narrow. In other words, the field I know well and love and know what to do. These other fields, if they're related, like graphene, or these 2-D materials, I think those take a lot of manpower because they are more unknown, so you need a student to go and just put things together and explore it. See if you could get a better layer. So, if I had more money, I could entertain having a student or some effort in some new area like that because I think they are fruitful. The trouble I have is that the MBE and this field are so expensive that I can't dilute myself. Because of that, I have never wandered too far off, because then we can't be so good at what we do. But yeah, I mean, it's hard to judge. I think it's a big field, and I don't know if anybody knows. High energy physics, I'm not an expert, so I don't know what is -- but in solid state, right now, quantum computing is a huge thing. Everybody wants to do it. I think it's a mistake to put every dollar into just that one field. I think it is better to fund it to some degree but allow for funding other things too. You essentially learn physics as you're trying to do the quantum computing.
It's like you said, back in 1986, everybody left and then they came back.
Right, yes. Quantum computing, I think it's somewhat similar, but it's a much bigger field. In those days, graphite intercalation, maybe there were twenty or thirty people working on it in the U.S. Then, maybe fifteen of them left, and some of them came back. Right now, there are many, many people working on quantum computing, so I don't think it will go away. This field is going to stay because industry has a lot of interest, and the government. They want to make sure they have security with the encryption. So, I don't think that will go away. My point is if you forget everything else, it's a problem. Quantum computing is not going to solve all problems.
Your lab will still be going strong.
Yes, I hope so.
I hope so. Well, Mansour, it's been an absolute pleasure speaking with you today. I'm so glad that we connected, and I want to thank you for spending this time with me.
Sure, thank you so much.