Valley-polarized quantum anomalous Hall phase and disorder induced valley-filtered chiral edge channels

TL;DR

This paper explores the valley-polarized quantum anomalous Hall phase, revealing how topological transitions occur via skyrmion formation and demonstrating robust, valley-filtered chiral edge channels even under disorder, with tunable phases in bilayer systems.

Contribution

It uncovers the mechanism of topological phase transition to VQAH and shows disorder-induced valley filtering, extending understanding of topological phases with multiple layers.

Findings

Topological phase transition involves skyrmion formation at valley gap closure.

Valley-filtered chiral edge channels remain robust under moderate disorder.

Bilayer systems exhibit tunable topological phases via interlayer bias.

Abstract

We investigate the topological and transport properties of the recently discovered valley-polarized quantum anomalous Hall (VQAH) phase. In single layer, the phase is realized through the competition between two types of spin-orbit coupling, which breaks the symmetry between the two valleys. We show that the topological phase transition from conventional quantum anomalous Hall phase to the VQAH phase is due to the change of topological charges with the generation of additional skyrmions in the real spin texture, when the band gap closes and reopens at one of the valleys. In the presence of short range disorders, pairs of the gapless edge channels (one from each valley in a pair) would be destroyed due to intervalley scattering. However, we discover that in an extended range of moderate scattering strength, the transport through the system is quantized and fully valley-polarized, i.e. the system is equivalent to a quantum anomalous Hall system with valley-filtered chiral edge channels. We further show that with additional layer degree of freedom, much richer phase diagram could be realized with multiple VQAH phases. For a bilayer system, we demonstrate that topological phase transitions could be controlled by the interlayer bias potential.