An Anderson impurity interacting with the helical edge states in a quantum spin Hall insulator

TL;DR

This paper investigates how a local magnetic impurity interacts with and is screened by the helical edge states in a quantum spin Hall insulator using the natural orbitals renormalization group method, revealing a clear Kondo screening process.

Contribution

It introduces the natural orbitals renormalization group method to analyze impurity screening in quantum spin Hall insulators, providing new insights into the Kondo effect in this context.

Findings

Local spin forms at the impurity site and is fully screened by edge electrons.

Screening is dominated by a single active natural orbital.

Kondo resonance peak observed in the local density of states.

Abstract

Using the natural orbitals renormalization group (NORG) method, we have investigated the screening of the local spin of an Anderson impurity interacting with the helical edge states in a quantum spin Hall insulator. We find that there is a local spin formed at the impurity site and the local spin is completely screened by electrons in the quantum spin Hall insulator. Meanwhile, the local spin is screened dominantly by a single active natural orbital. We then show that the Kondo screening mechanism becomes transparent and simple in the framework of natural orbitals formalism. We project the active natural orbital respectively into real space and momentum space to characterize its structure. And we confirm the spin-momentum locking property of the edge states based on the occupancy of a Bloch state in the edge to which the impurity couples. Furthermore, we study the dynamical property of the active natural orbital represented by the local density of states, from which we observe the Kondo resonance peak.