Suppressing backscattering of helical edge modes with a spin bath

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.