Kondo effect in the helical edge liquid of the quantum spin Hall state

TL;DR

This paper investigates how magnetic impurities affect the edge conductance of quantum spin Hall insulators, revealing temperature-dependent behaviors and novel tunneling phenomena linked to the Kondo effect and electron interactions.

Contribution

It provides a theoretical analysis of impurity effects on QSH edge conductance, highlighting the role of interactions and revealing unique low-temperature tunneling behavior.

Findings

Logarithmic temperature dependence at high temperatures due to Kondo effects

Restoration of conductance at low temperatures with power-law behavior

Weak tunneling involving half-electron charge transfer in strongly interacting regimes

Abstract

Following the recent observation of the quantum spin Hall (QSH) effect in HgTe quantum wells, an important issue is to understand the effect of impurities on transport in the QSH regime. Using linear response and renormalization group methods, we calculate the edge conductance of a QSH insulator as a function of temperature in the presence of a magnetic impurity. At high temperatures, Kondo and/or two-particle scattering give rise to a logarithmic temperature dependence. At low temperatures, for weak Coulomb interactions in the edge liquid the conductance is restored to unitarity with unusual power-laws characteristic of a `local helical liquid', while for strong interactions transport proceeds by weak tunneling through the impurity where only half an electron charge is transferred in each tunneling event.