Disorder-Induced Weyl Semimetal Phase and Sequential Band Inversions in PbSe-SnSe Alloys

TL;DR

This study demonstrates that disorder in PbSe-SnSe alloys can induce a Weyl semimetal phase through sequential band inversions and valley splitting, revealing topological properties in low-symmetry, disordered systems.

Contribution

It provides a fully-atomistic topological analysis showing disorder can create Weyl phases without external magnetic fields in alloys.

Findings

Valley degeneracy is removed by disorder, causing band splitting over a range of compositions.

A Weyl semimetal phase emerges naturally in the alloy without external magnetic fields.

Sequential band inversions occur as a function of alloy composition.

Abstract

The search for topological systems has recently broadened to include random substitutional alloys, which lack the specific crystalline symmetries that protect topological phases, raising the question whether topological properties can be preserved, or are modified by disorder. To address this question, we avoid methods that assumed at the outset high (averaged) symmetry, using instead a fully-atomistic, topological description of alloy. Application to PbSe-SnSe alloy reveals that topology survives in an interesting fashion: (a) spatial randomness removes the valley degeneracy (splitting larger than 150 meV), leading to a sequential inversion of the split valley components over a range of compositions; (b) absence of inversion lifts spin degenerates, leading to a Weyl semimetal phase without the need of external magnetic field, an unexpected result, given that the alloy constituent compounds are inversion-symmetric. (a) and (b) underpin the topological physics at low symmetry and complete the missing understanding of possible topological phases within the normal-topological insulator transition.