Coulomb drag between helical edge states

TL;DR

This paper theoretically studies Coulomb drag between helical edge states in quantum spin Hall systems, revealing it vanishes at second order but becomes finite with a magnetic field, showing unique magnetic field dependence.

Contribution

It introduces a novel theoretical analysis of Coulomb drag in helical edge states, highlighting the absence of backscattering effects and the magnetic field dependence.

Findings

Drag vanishes at second order in absence of magnetic field

Finite drag scales as the fourth power of magnetic field

Temperature dependence characterized for different edge dispersions

Abstract

We theoretically investigate the Coulomb drag between the edge states of two quantum spin Hall systems. Using an interacting theory of the one-dimensional helical edge modes, we show that the drag vanishes at second order in the inter-edge interaction, where it is typically finite in other systems, due to the absence of backscattering within the edges. However, in the presence of a small external magnetic field the drag is finite and scales as the fourth power of the magnetic field, a behavior that sharply distinguishes it from other systems. We obtain the temperature dependence of the drag for regimes of both linear and quadratic edge dispersion in the presence of a finite field.