Topological linelike bound states in the continuum

TL;DR

This paper introduces a new type of topologically protected bound states in the continuum (BIC) that appear as lines in momentum space, expanding the understanding of topological states beyond point-like BICs.

Contribution

It proposes a topological BIC protected by the winding number, realized in a multilayer honeycomb lattice model, and explains their appearance through momentum space topology.

Findings

BIC appear as lines in momentum space.

Wave numbers of BIC are explained by topology.

Band structure and localization are demonstrated.

Abstract

Bound states in the continuum (BIC) have been studied mainly in optics. Recently, electronic BIC have been proposed. They appear as points in the momentum space and are protected topologically by the Chern number. In this study, we propose a type of BIC protected by the winding number, which is one of the topological invariants. These BIC appear as lines in the momentum space, and are realized in a multilayer model consisting of honeycomb-lattice layers. We show band structure and spatial localization of the BIC in this model. The wave numbers at which the BIC appear can be explained in terms of topology in the momentum space.