Magnetochiral anisotropy on a quantum spin Hall edge

TL;DR

This paper develops a theoretical model for magnetochiral anisotropy in quantum spin Hall edges, explaining nonlinear transport phenomena influenced by magnetic fields and bulk states, with validation against experiments on WTe2.

Contribution

The paper introduces a novel theory describing nonlinear magnetotransport on quantum spin Hall edges, emphasizing two mechanisms of magnetochiral anisotropy involving interactions and dispersion modifications.

Findings

Good agreement with experiments on monolayer WTe2

Identification of two mechanisms for magnetochiral anisotropy

Prediction of bias-dependent resistance in edge states

Abstract

We develop a theory of nonlinear low-magnetic-field magnetotransport on a helical edge of a quantum spin Hall insulator due to the edge state coupling to bulk midgap states. We focus on the part of the nonlinear I-V characteristic that is odd in the applied magnetic field, and quadratic in the applied bias voltage. This part of the I-V characteristic corresponds to the resistance of the sample being dependent on the relative orientation of the current and an external magnetic field, hence represents a type of edge magnetochiral anisotropy. We identify two mechanisms of the magnetochiral anisotropy. One is related to the Hubbard interaction on the midgap state, which leads to the dependence of the scattering characteristics on the current flowing on the edge, which results in bias-voltage-dependent resistance, or equivalently conductance, hence a nonlinear I-V. The other is related to the modification of the edge dispersion by a magnetic field, and requires nonlinearity in the edge dispersion. We compare the developed theory to the experiments on monolayer $\mathrm{WTe}_{2}$, and find good agreement with the developed theory.