Current-induced reversal of anomalous Hall conductance in twisted bilayer graphene

TL;DR

This paper presents a theoretical explanation for how a dc electric current can switch the valley polarization and topological state in twisted bilayer graphene, explaining experimental observations of Hall conductance reversal.

Contribution

It introduces a theory showing that bulk current redistributes electron occupation, deforming bands and causing a topological switch in TBG.

Findings

Current causes redistribution of electrons near the Fermi level.

Band deformation and shifting lead to valley polarization switching.

Above a critical current, the topological state is reversed.

Abstract

It is observed experimentally that the sign of the Hall resistance can be flipped by a dc electric current in the twisted bilayer graphene (TBG) at 3/4 filling of the four-fold degenerate conduction flat bands. The experiment implies a switching of the valley polarization (VP) and topology in TBG. Here we present a theory on the current-induced switching of VP and topology. The presence of current in the bulk causes {the} redistribution of {electron occupation} in bands near the Fermi energy, which then deforms and shifts the band dispersion due to the Coulomb interaction. Above a critical current, the original occupied and empty bands can be swapped resulting in the switching of VP and topology.