Exchange-Driven Intermixing of Bulk and Topological Surface State by Chiral Excitons in Bi2Se3

TL;DR

This study uses ab initio calculations to reveal how exchange-driven chiral excitons in Bi2Se3 cause intermixing of bulk and topological surface states, impacting optical properties and topological protection.

Contribution

It uncovers the role of exchange-driven chiral excitons in mixing bulk and surface states, providing new insights into electron-hole interactions in topological insulators.

Findings

Identification of multiple chiral excitons with bulk and surface character

Exchange-driven mixing relaxes topological protection

Implications for optical response and circular polarization

Abstract

Topological surface states (TSS) in the prototypical topological insulator (TI) Bi2Se3 are frequently characterized using optical probes, but electron-hole interactions and their effect on surface localization and optical response of the TSS remain unexplored. Here, we use ab initio calculations to understand excitonic effects in the bulk and surface of Bi2Se3. We identify multiple series of chiral excitons that exhibit both bulk and TSS character, due to exchange-driven mixing. Our results address fundamental questions about the degree to which electron-hole interactions can relax the topological protection of surface states and dipole selection rules for circularly polarized light in TIs by elucidating the complex intermixture of bulk and surface states excited in optical measurements and their coupling to light.