Helical bound states in the continuum of the edge states in two dimensional topological insulators

TL;DR

This paper investigates the emergence of bound states in the continuum within the edge states of two-dimensional topological insulators, revealing helical structures and resonance interference effects caused by structural defects.

Contribution

It introduces the concept of helical bound states in the continuum in 2D topological insulators and analyzes their formation conditions and spatial electron density distribution.

Findings

Bound states in the continuum can form due to resonance interference.

The BIC exhibits a helical electron current around defects.

Conditions for BIC appearance are explicitly derived.

Abstract

We study bound states embedded into the continuum of edge states in two-dimensional topological insulators. These states emerge in the presence of a short-range potential of a structural defect coupled to the boundary. In this case the edge states flow around the defect and have two resonances in the local density of states. The bound state in continuum (BIC) arises due to an interference of the resonances when they are close to the degeneracy. We find the condition under which the BIC appears, study the spacial distribution of the electron density, and show that the BIC has a helical structure with an electron current circulating around the defect.