Quantum Hall Superconductivity from Moir{\'e} Landau Levels

TL;DR

This paper proposes that twisted bilayer graphene at a magic angle can exhibit reentrant superconductivity above the upper critical field due to Landau level quantization, supported by a theoretical model.

Contribution

It introduces a theoretical framework suggesting quantum Hall superconductivity in MATBG, highlighting its unique Landau level degeneracy and potential for experimental observation.

Findings

Landau levels in MATBG are doubly degenerate.

Superconductivity can reappear above the critical field due to Landau quantization.

Obstacles include disorder, thermal fluctuations, and competing phases.

Abstract

It has long been speculated that quasi-two-dimensional superconductivity can reappear above its semiclassical upper critical field due to Landau quantization, yet this reentrant property has never been observed. Here, we argue that twisted bilayer graphene at a magic angle (MATBG) is an ideal system in which to search for this phenomenon because its Landau levels are doubly degenerate, and its superconductivity appears already at carrier densities small enough to allow the quantum limit to be reached at relatively modest magnetic fields. We study this problem theoretically by combining a simplified continuum model for the electronic structure of MATBG with a phenomenological attractive pairing interaction, and discuss obstacles to the observation of quantum Hall superconductivity presented by disorder, thermal fluctuations, and competing phases.