A non-magnetic mechanism of backscattering in helical edge states

TL;DR

This paper proposes a non-magnetic, interaction-driven backscattering mechanism in helical edge states of topological insulators, involving zero-mode fluctuations in a nearby puddle, which explains temperature-independent backscattering rates observed experimentally.

Contribution

It introduces a novel backscattering mechanism based on puddle zero-mode fluctuations, without involving magnetic impurities or inelastic scattering, advancing understanding of edge state robustness.

Findings

Backscattering rate is temperature-independent above puddle level spacing.

Zero-mode fluctuations induce effective magnetic flux, enabling backscattering.

The mechanism aligns with recent experimental observations.

Abstract

We study interaction-induced backscattering mechanism for helical edge states of a two-dimensional topological insulator which is tunnel-coupled to a puddle located near the edge channel. The mechanism does not involve inelastic scattering and is due to the zero-mode fluctuations in a puddle. We discuss in detail a simple model of a puddle - a cavity in the bulk of the topological insulator. Such a cavity also has helical edge states with tunneling coupling to helical states encompassing the topological insulator. We analyze effect of the edge current in the puddle. Although averaged value of this current is equal to zero, its zero-mode fluctuations act, in the presence of electron-electron interaction, similar to magnetic flux thus allowing backscattering processes, which involve tunneling through the puddle. Rectification of these fluctuations leads to a finite probability of backscattering. This effect is further enhanced due to dephasing process which is also dominated by zero-mode fluctuations. Remarkably, for temperature exceeding level spacing in the puddle, the rate of backscattering does not depend on temperature in a good agreement with recent experiments.