Finite-size topological phases from semimetals

TL;DR

This paper reveals that thin films of Weyl semimetals exhibit unique finite-size topological phases with coexisting bulk and boundary signatures, expanding the understanding of topological phases in reduced dimensions.

Contribution

The study introduces a new class of finite-size topological phases in Weyl semimetal thin films, characterized by a novel bulk-boundary correspondence not captured by existing classification schemes.

Findings

Finite-size Weyl semimetal films host unique topological phases.

These phases feature coexisting 3D bulk responses and boundary states.

Experimental Hamiltonians for MoTe2 demonstrate these phases.

Abstract

Topological semimetals are some of the topological phases of matter most intensely-studied experimentally. The Weyl semimetal phase, in particular, has garned tremendous, sustained interest given fascinating signatures such as the Fermi arc surface states and the chiral anomaly, as well as the minimal requirements to protect this three-dimensional topological phase. Here, we show that thin films of Weyl semimetals (which we call quasi-(3-1)-dimensional, or q(3-1)d) generically realize finite-size topological phases distinct from 3d and 2d topological phases of established classification schemes: response signatures of the 3d bulk topology co-exist with topologically-protected, quasi-(3-2)d Fermi arc states or chiral boundary modes due to a second, previously-unidentified bulk-boundary correspondence. We show these finite-size topological semimetal phases are realized by Hamiltonians capturing the Fermiology of few-layer Van der Waals material MoTe2 in experiment. Given the broad experimental interest in few-layer Van der Waals materials and topological semimetals, our work paves the way for extensive future theoretical and experimental characterization of finite-size topological phases.