Topological Superconductivity in Twisted Multilayer Graphene

TL;DR

This paper investigates topological superconductivity in twisted multilayer graphene, revealing that valley degrees of freedom favor spin triplet $d+id$ pairing states that are topologically nontrivial with protected edge states.

Contribution

It introduces a minimal Hubbard model for superconductivity in twisted graphene multilayers, highlighting the role of valley degrees of freedom in stabilizing topological triplet pairing states.

Findings

Identification of valley singlet $d+id$ pairing states

Both states are topological superconductors

Support for half-vortices with protected edge states

Abstract

We study a minimal Hubbard model for electronically driven superconductivity in a correlated flat mini-band resulting from the superlattice modulation of a twisted graphene multilayer. The valley degree of freedom drastically modifies the nature of thepreferred pairing states, favoring spin triplet $d+id$ order with a valley singlet structure. We identify two candidates in this class, which are both topological superconductors. These states support half-vortices carrying half the usual superconducting flux quantum $hc/(4e)$, and have topologically protected gapless edge states.