Suppressing backscattering of helical edge modes with a spin bath

TL;DR

This paper investigates how interactions with an external spin bath affect the stability of helical edge modes in topological insulators, revealing conditions under which backscattering can be suppressed to preserve edge state protection.

Contribution

It introduces a framework analyzing the interplay of Coulomb and spin-spin interactions with helical edge modes, showing how a spin bath can stabilize protected chiral states.

Findings

Coulomb interactions amplify backscattering, destabilizing edge modes.

Spin-spin interactions marginally suppress backscattering.

Combined interactions can render backscattering irrelevant, restoring protection.

Abstract

In this paper, we address the question of stability of protected chiral modes (e.g., helical edge states at the boundary of two-dimensional topological insulators) upon interactions with the external bath. Namely, we study how backscattering amplitude changes when different interaction channels between the system and the environment are present. Depending on the relative strength of the Coulomb and spin-spin channels, we discover three different possible regimes. While the Coulomb interaction on its own naturally amplifies the backscattering and destroys the protection of chiral modes, and the spin-spin channel marginally suppresses backscattering, their interplay can make the backscattering process strictly irrelevant, opening the possibility to use the external spin bath as a stabilizer that alleviates destructive effects and restores the chirality protection.