Physics & Astronomy Colloquium – Spring 2020 – Rossi
April 1 @ 3:30 pm - 5:00 pm
Speaker: Enrico Rossi (William & Mary)
Title: SUPERCONDUCTIVITY AND QUANTUM METRIC IN MAGIC-ANGLE TWISTED BILAYER GRAPHENE
Abstract: Graphene, an atom thick layer of carbon atoms, was first isolated in 2004. By now its electronic properties are very well known; in particular it is well known that graphene does not have any tendency to be a superconductor. However, in the last two years experimentalists have shown that a system formed by two layers of graphene, when stacked with a specific –“magic”– relative twist angle, can become superconducting. One of the key features of magic-angle twisted bilayer graphene is the fact that its electronic bands are extremely flat. The flat nature of the bands favors the formation of electronic collective ground states. However, standard results suggest that for a system with flat bands superconductivity could be observed only at vanishingly small temperatures. This is not the case in magic-angle twisted bilayer graphene. In this talk I will first introduce the key properties of “magic-angle twisted bilayer graphene”. I will then discuss how it is possible for such a system to show all the hallmarks of superconductivity despite the fact that, due to the extreme flatness of the bands, results valid for standard superconductors would lead to conclude that the macroscopic signatures of superconductivity should be absent. I will show that this is due to the connection between superconductivity and the quantum metric of the flat bands.
Geometric and conventional contribution to superfluid weight in twisted bilayer graphene, Xiang Hu, Timo Hyart, Dmitry I. Pikulin, Enrico Rossi, Phys. Rev. Lett, 123, 237002 (2019)
Speaker Biography: Enrico Rossi is an associate professor of physics at William & Mary (Williamsburg VA). He received his B.S. from the Turin Polytechnic in Italy, and his Ph.D. in physics from the University of Texas at Austin. After earning his PhD. he was a postdoctoral research associate at the University of Illinois at Chicago between 2005 and 2007 and then at the Condensed Matter Theory Center at the university of Maryland until 2010, when he joined the physics faculty at William & Mary. His research focuses on the electronic properties of low-dimensional systems, two-dimensional heterostructures, topological systems, and topological superconductors supporting non-abelian fermionic states. In 2017 he was a visiting researcher at Microsoft Station Q in Santa Barbara. He was awarded an NSF Faculty Early Career Award (CAREER) and is a recipient of the 2017 Plumeri Award for Faculty Excellence.