By A Fish  

LEXINGTON; Ky. — Moiré electronics are hot topics for theoretical physics. Ganpathy Murthy, professor of physics and astronomy in the University of Kentucky’s College of Arts & Sciences, spoke about the upcoming van Winter Lecture and about guest lecturer Ashvin Vishwanath, a theoretical physicist specializing in the study of condensed matter at Harvard University. 

Vishwanath is a condensed matter theorist who studies collective phenomena in quantum systems. His previous research has explored the central role of "hedgehog" defects in phase transitions, the occurrence of distinctive surface states in Weyl semimetals, Dirac fermion dualities and the notion of surface topological order.  

His attention is focused on unraveling the mysteries of moiré materials and exploring ways to create highly entangled states in synthetic quantum platforms. Vishwanath was born and raised in Bangalore, India, and earned his undergraduate degree in physics from the Indian Institute of Technology-Kanpur. He then moved to Princeton University for his doctorate under Duncan Haldane, following which he held a Pappalardo postdoctoral fellowship at MIT and then moved on to a faculty position at the University of California, Berkeley.  

He spent 12 years on the faculty at UC Berkeley before moving to his current position in 2016 as professor of physics at Harvard University. He is also the director of the Simons Collaboration on Ultra Quantum Matter. He has been awarded the Sloan and Guggenheim Fellowships, the 2016 Europhysics Prize and was elected to the American Academy of Arts and Sciences in 2021. 

Vishwanath will discuss moiré electronics in a lecture titled “Quantum Computing and the Entanglement Frontier” The lecture will be from 4 to 5 p.m. in Chemistry-Physics Building 155 on the UK campus.  

Q: What is the van Winter Lecture, and how did the tradition begin? 

Murthy: The van Winter lecture is a memorial that is named after one of our former faculty members, Clasine van Winter. She was a faculty member here until about 1999. Then she retired and died in 2000. In her memory, the department created an annual named lecture. She was a mathematical physicist; this means that she worked on the more mathematical end of theoretical physics. She used to prove theorems about things that happen in physics. Because she was a mathematical physicist, she had appointments in both the mathematics department and in our physics department. The van Winter lecture is jointly sponsored by the Mathematics Department and the Physics and Astronomy Department. What we do is we try to invite people who work is of interest to people in both departments.  

Q: Who do you have coming to lecture this year? 

Murthy: This year it is the turn of the Physics and Astronomy Department to invite a lecturer.  We asked Ashwin Vishwanath. Ashwin is a condensed matter theoretical physicist, and what that means is that he works in the area of solid-state physics or what used to be called solid-state physics, and has to do with systems with a very large number of electrons and how the electrons behave -- particularly at very low temperatures and under some other extreme conditions such as high magnetic fields and so on. Ashwin is in his late 40s, and he is a star in condensed matter physics. He's a star in theoretical physics in general. He got his PhD at Princeton and was a postdoc at MIT. He was a faculty member at the University of California at Berkeley for more than a decade, and then not so long ago he went to Harvard. Since then, his publication rate and the ideas that he generates have just taken off. 

Q: What is Vishwanath’s lecture going to be about? 

Murthy: He's made several contributions. He was one of the discoverers of something known as topological semi metals in 2011. More recently, there has been a revolution driven by experiments in moiré electronics and moiré materials. A moiré pattern is something that happens when you overlay two slightly different periodic patterns on top of each other. If you lay two silks on top of each other, there's an interference pattern that they form, and you can see a larger scale pattern emerging. 

What he's going to talk about is two sheets of carbon, which are called graphene. Each single sheet of carbon is graphene, so if you think of graphite, it's made of these layers, and you can peel off these layers and each layer is called graphene. You can lay down two of these sheets, and you twist them slightly with respect to each other before you put them together, and then they form a Moiré pattern, except on a much tinier scale than you could ever see with your naked eye. These materials have some really remarkable properties.  It is made of nothing but carbon, but experimentally it was shown in 2018 that such materials can form superconductors and certain special types of insulators. 

Q: What is the goal of these lectures? 

Murthy: What we're really hoping is that the mathematicians see something beautiful about the kind of physics that goes on. Then the physicists can come and say you know, hey, this has some relevance to what I'm thinking about and so on. We want to really bring the physics and the mathematics community together. What we suggest to the speakers is that they pitch at least the introduction at a more basic level so that people who are even outside the community can attend it, and we want to encourage the broader university community to come to this and then get something out of this annual event.