Isabelle Phinney

Harvard University, Kim group

Title: Introduction to Twisted Multilayer Graphene

Abstract: 

Since the 2018 discovery of superconductivity in twisted bilayer graphene (TBG), the field of twisted graphene, and, generally, moiré systems, has exploded[1][2]. Twisted graphene systems offer highly tunable narrow electronic bands, which easily lend themselves to the study of strongly correlated physics. Many interesting phases have been observed in these flat band systems, including superconductivity, correlated insulators, and ferromagnetism, all of which are likely tied to the correlated electron interactions. The family of moiré graphene was recently extended beyond bilayer to include multilayer systems [3][4][5][6]. Unlike in TBG, the superconductivity in multilayer systems is electric field tunable and exhibits an in-plane critical field approximately 3 times larger than that of the Pauli limit for conventional BCS superconductors. Experimental evidence of superconductivity in this “family” of twisted graphene strongly suggests the existence of unconventional superconductivity in all multilayer moiré graphene systems, raising questions about the common nature of this unusual superconductivity. In this talk, I will provide an overview of moiré physics, and discuss twisted multilayers and our efforts to understand the open questions about the relationship between symmetry-breaking, band structure, and superconductivity in these systems.

The large number of different phases accessible in twisted graphene systems also lends itself to both vertical and lateral heterostructure design. I would like to have an informal discussion at the end of the talk about potential applications as well as the advantages (and challenges) moiré systems bring to this kind of engineering.