Spontaneous gap generation on the surface of weakly interacting topological insulators using nonmagnetic impurities

TL;DR

This paper demonstrates that nonmagnetic impurities on the surface of weakly interacting topological insulators can induce local magnetization and a global energy gap, even with weak Coulomb interactions, due to impurity-induced resonance effects.

Contribution

It reveals that nonmagnetic impurities significantly lower the threshold for magnetic order and gap formation on TI surfaces, a novel mechanism for gap generation.

Findings

Impurities induce local magnetization on TI surfaces.

A global energy gap forms linearly with maximum local magnetization.

Weak interactions can produce magnetic states due to impurity effects.

Abstract

Strong nonmagnetic impurities on the surface of three-dimensional topological insulators (TIs) generate localized resonance peaks close to the Dirac point. We show that this results in a strongly reduced critical Coulomb interaction strength to reach a magnetic surface state, following a Stoner-like criterion. Thus even weakly interacting TIs host a finite (local) magnetization around strong nonmagnetic impurities. The local magnetization gives rise to a global energy gap, linearly dependent on the maximum value of the magnetization but decreasing with reduced impurity concentration.