Chiral Topological Excitons in a Chern Band Insulator

TL;DR

This paper demonstrates that Chern band insulators can host topologically non-trivial exciton bands with chiral edge modes, which can be observed through optoelectronic responses, expanding the understanding of topological states in semiconductors.

Contribution

It introduces the concept of topological excitons in Chern insulators and calculates their Chern numbers using a two-band model, proposing experimental detection methods.

Findings

Exciton bands with non-zero Chern integers are found in Chern insulators.

Chiral exciton edge modes can be detected via non-local optoelectronic responses.

Potential material platforms include HgTe, InAs/GaSb quantum wells, and (Bi,Sb)₂Te₃ thin films.

Abstract

A family of semiconductors called as Chern band insulator are shown to host exciton bands with non-zero topological Chern integers and chiral exciton edge modes. Using a prototypical two-band Chern insulator model, we calculate a cross-correlation function to obtain the exciton bands and their Chern integers. The lowest exciton band acquires Chern integers such as $\pm 1$ and $\pm 2$ in electronic Chern insulator phase. The non-trivial topology can be experimentally observed both by non-local optoelectronic response of exciton edge modes and by a phase shift in the cross-correlation response due to the bulk mode. Our result suggests that magnetically doped HgTe, InAs/GaSb quantum wells and $\text{(Bi,Sb)}_{2} \text{Te}_{3}$ thin film are promising candidates for a platform of topological excitonics.