Backscattering in helical edge states from a magnetic impurity and Rashba disorder

TL;DR

This paper investigates how magnetic impurities and Rashba disorder affect backscattering in helical edge states of quantum spin Hall insulators, explaining experimental observations of conductance behavior.

Contribution

It introduces a model combining magnetic impurities with Rashba disorder to explain backscattering and conductance fluctuations in helical edge states.

Findings

Impurity-induced resistance matches experimental temperature dependence.

Elastic backscattering and interference explain conductance oscillations.

Model accounts for weak temperature dependence of mean free path.

Abstract

Transport by helical edge states of a quantum spin Hall insulator is experimentally characterized by a weakly temperature-dependent mean free path of a few microns and by reproducible conductance oscillations, challenging proposed theoretical explanations. We consider a model where edge electrons experience spatially random Rashba spin-orbit coupling and couple to a magnetic impurity with spin S >= 1/2. In a finite bias steady state, we find for S > 1/2 an impurity induced resistance with a temperature dependence in agreement with experiments. Since backscattering is elastic, interference between different scatterers possibly explains conductance fluctuations.