Elastic backscattering of quantum spin Hall edge modes from Coulomb interactions with non-magnetic impurities

TL;DR

This paper shows that Coulomb interactions with dynamical impurities can cause quasi-elastic backscattering in quantum spin Hall edge modes without breaking time-reversal symmetry, affecting electrical resistance.

Contribution

It introduces a new backscattering mechanism involving dynamical impurities modeled as two-level systems, expanding understanding of edge mode transport.

Findings

Backscattering occurs without magnetic impurities or electron tunneling.

Resistance exhibits weak temperature dependence.

Mechanism preserves time-reversal symmetry.

Abstract

We demonstrate that electrostatic interactions between helical electrons at the edge of a quantum spin Hall insulator and a dynamical impurity can induce quasi-elastic backscattering. Modelling the impurity as a two-level system, we show that transitions between counterpropagating Kramers-degenerate electronic states can occur without breaking time-reversal symmetry, provided that the impurity also undergoes a transition. The associated electrical resistance has a weak temperature dependence down to a non-universal temperature scale. Our results extend the range of known backscattering mechanisms in helical edge modes to include scenarios where electron tunnelling out of the system is absent.