Fingerprints of Berry phases in the bulk exciton spectrum of a topological insulator

TL;DR

This paper investigates how Berry phases influence the bulk exciton spectrum in topological insulators, revealing distinct spectral fingerprints that differentiate topological from trivial phases through semiclassical and quantum models.

Contribution

It demonstrates the impact of Berry phases on excitonic spectra in topological insulators, linking topological properties to observable spectral features.

Findings

Berry phase affects exciton spectrum significantly in topological regime

Spectral degeneracies are broken due to Berry phase effects

Numerical simulations confirm qualitative predictions

Abstract

We examine excitons formed in the bulk of a topological insulator as the system is tuned via a parameter between topological and trivial insulating phases, arguing that nontrivial topology has fingerprints in the spectrum of these excitons. The closely related hydrogen atom problem is well known to have a degeneracy due to a hidden symmetry, and the changes to the excitonic spectrum that we find can be understood as a result of breaking of this underlying symmetry due to the Berry phase. Furthermore, this phase is found to affect the spectrum in the topological parameter regime much more strongly than in the trivial regime. We first construct a semiclassical model of the system to develop qualitative intuition for the effects at play, then move to a more robust numerical simulation of the full quantum system, working with the Bernevig-Hughes-Zhang model of a 2D topological insulator.