Kondo screening by the surface modes of a strong topological insulator

TL;DR

This paper investigates how magnetic impurities on the surface of strong topological insulators are screened by surface electrons, revealing conditions for full screening and analyzing observable Friedel oscillations with six-fold symmetry.

Contribution

It introduces a mapping to an effective one-dimensional model considering Fermi line warping and uses mean-field theory to analyze Kondo screening and Friedel oscillations.

Findings

Impurity is fully screened except at the Dirac point.

Friedel oscillations exhibit six-fold symmetry in certain conditions.

Quantitative analysis for Bi2Se3 and Bi2Te3 compounds.

Abstract

We consider a magnetic impurity deposited on the surface of a strong topological insulator and interacting with the surface modes by a Kondo exchange interaction. Taking into account the warping of the Fermi line of the surface modes, we derive a mapping to an effective one dimensional model and show that the impurity is fully screened by the surface electrons except when the Fermi level lies exactly at the Dirac point. Using an Abrikosov fermion mean-field theory, we calculate the shape of the electronic density Friedel oscillation resulting from the presence of the Kondo screening cloud. We analyze quantitatively the observability of a six-fold symmetry in the Friedel oscillations for two prototype compounds: Bi$_2$Se$_3$ and Bi$_2$Te$_3$.