Disorder and metal-insulator transitions in Weyl semimetals

TL;DR

This paper investigates how disorder affects Weyl semimetals, revealing three unique phase transitions including from WSM to quantum anomalous Hall states and insulator-to-WSM transitions, supported by numerical phase diagram analysis.

Contribution

It uncovers three novel disorder-induced phase transitions in Weyl semimetals, expanding understanding of their topological and electronic properties under disorder.

Findings

Disorder can annihilate Weyl nodes, opening a topological gap.

Transitions from WSM to anomalous Hall metal or insulator are driven by disorder.

Phase diagram mapped using localization length and Hall conductivity calculations.

Abstract

The Weyl semimetal (WSM) is a newly proposed quantum state of matter. It has Weyl nodes in bulk excitations and Fermi arcs surface states. We study the effects of disorder and localization in WSMs and find three exotic phase transitions. (I) Two Weyl nodes near the Brillouin zone boundary can be annihilated pairwise by disorder scattering, resulting in the opening of a topologically nontrivial gap and a transition from a WSM to a three-dimensional (3D) quantum anomalous Hall state. (II) When the two Weyl nodes are well separated in momentum space, the emergent bulk extended states can give rise to a direct transition from a WSM to a 3D diffusive anomalous Hall metal. (III) Two Weyl nodes can emerge near the zone center when an insulating gap closes with increasing disorder, enabling a direct transition from a normal band insulator to a WSM. We determine the phase diagram by numerically computing the localization length and the Hall conductivity, and propose that the exotic phase transitions can be realized on a photonic lattice.