Anomalous quantum Hall effect induced by disorder in topological insulators

TL;DR

This paper studies how disorder induced by magnetic impurities causes a transition from a two-dimensional topological insulator to a Chern insulator with a different conductance, revealing a phase with G=1 even under ferromagnetic order.

Contribution

It demonstrates the existence of a G=1 phase under strong disorder for ferromagnetic coupling, supported by numerical and analytical methods, challenging previous mean field predictions.

Findings

A G=1 phase exists under strong disorder even with ferromagnetic order.

The transition involves suppression of one spin conduction channel due to disorder.

Numerical and analytical results confirm the disorder-induced phase transition.

Abstract

We investigate a transition between a two-dimensional topological insulator conduction state, characterized by a conductance $G=2$ (in fundamental units $e^2/h$) and a Chern insulator with $G=1$, induced by polarized magnetic impurities. Two kinds of coupling, ferro and antiferromagnetic, are considered with the electron and hole subbands. We demonstrate that for strong disorder, a phase $G=1$ exists even for ferromagnetic order, in contrast with the prediction of the mean field approximation. This result is supported by direct numerical computations using Landauer transport formula, and by analytical calculations of the chemical potential and mass renormalization as a function of the disorder strength, in the self-consistent Born approximation. The transition is related to the suppression of one of the spin conduction channels, for strong enough disorder, by selective spin scattering and localization.