Conductance of a helical edge liquid coupled to a magnetic impurity

TL;DR

This paper investigates how a magnetic impurity affects electrical and thermal conductance in a quantum spin Hall edge, revealing no correction to electrical conductance but a finite correction to thermal conductance due to spin-flip backscattering.

Contribution

It demonstrates that isotropic Kondo exchange causes no dc electrical conductance correction but introduces a finite thermal conductance correction in helical edge liquids.

Findings

Electrical conductance remains universal in the dc limit.

Thermal conductance is affected by magnetic impurities.

Spin-flip backscattering influences thermal transport.

Abstract

Transport in an ideal two-dimensional quantum spin Hall device is dominated by the counterpropagating edge states of electrons with opposite spins, giving the universal value of the conductance, $2e^2/h$. We study the effect on the conductance of a magnetic impurity, which can backscatter an electron from one edge state to the other. In the case of isotropic Kondo exchange we find that the correction to the electrical conductance caused by such an impurity vanishes in the dc limit, while the thermal conductance does acquire a finite correction due to the spin-flip backscattering.