Debanjan Chowdhury
Inspired by the discovery of superconductivity in moiré materials, I will discuss the long-standing problem on whether superconductivity can exist if the electrons’ kinetic energy is completely quenched. This is fundamentally a nonperturbative problem, since the interaction energy scale is the only relevant energy scale, and requires going beyond the traditional Bardeen-Cooper-Schrieffer theory of superconductivity. In the first part of the talk, I will discuss the problem of an interacting two-dimensional system with narrow topological bands using numerically exact quantum Monte Carlo calculations. In the second part of my talk, I will discuss the more realistic problem of magic-angle twisted bilayer graphene with electron-phonon interactions. In particular, I will show that certain umklapp processes, which arise physically as a result of the zone folding due to the moiré superlattice structure, contribute significantly towards enhancing pairing. I will comment on the effect of external screening due to a metallic gate on superconductivity and propose a smoking-gun experiment to detect resonant features associated with the phonon-umklapp processes in the differential conductance.