Quantum Anomalous Hall Effect in Ferromagnetic Metals

TL;DR

This paper theoretically demonstrates the realization of the quantum anomalous Hall effect in ferromagnetic metals, expanding its occurrence beyond insulators and revealing unique conductive properties and robustness to disorder.

Contribution

It introduces a new metallic phase exhibiting the QAH effect with coexistence of chiral edge channels and bulk conduction, distinct from traditional insulating QAH phases.

Findings

QAH effect can occur in metallic systems without a bulk energy gap.

Quantized Hall conductivity can emerge due to dephasing despite non-quantized Hall resistivity.

The metallic QAH phase shows robustness against disorder.

Abstract

The quantum anomalous Hall (QAH) effect holds fundamental importance in topological physics and technological promise for electronics. It is generally believed that the QAH effect can only be realized in insulators. In this Letter, we theoretically demonstrate that the QAH effect can also be realized in metallic systems, representing a phase distinct from the conventional QAH phase in insulators. This phase is characterized by the coexistence of chiral edge channels and isotropic bulk conduction channels without a bulk energy gap. Notably, in a six-terminal Hall bar, our calculations show that, the quantized Hall conductivity and nonzero longitudinal conductivity can emerge due to dephasing, despite the Hall resistivity itself never becoming quantized. Furthermore, the quantized Hall conductivity exhibits remarkable robustness against disorder. Our findings not only extend the range of materials capable of hosting the QAH effect from insulators to metals, but also provide insights that may pave the way for the experimental realization of the QAH effect at elevated temperatures.