Interplay of Excitonic and Topological Effects in few-layer Bi₂Te₃

The interplay between quasiparticle band topology and excitonic effects has recently attracted significant attention, particularly in the context of chiral excitons in bulk topological insulators and topological excitons emerging from bands with opposite Chern numbers. However, a full microscopic understanding of how topology influences exciton energies, optical selection rules, and exciton band dispersion remains lacking. Bi₂Te₃, a prototypical strong topological insulator in the bulk, offers a unique platform since in its few-layer forms, particularly two-quintuple-layer, is predicted to be a two-dimensional topological insulator with inversion symmetry. Using ab initio GW plus Bethe-Salpeter equation calculations, we investigate the evolution of excitonic properties as the system undergoes a spin-orbit-induced topological phase transition. We analyze exciton envelope functions, selection rules, and exciton band topology, revealing how band inversion reshapes the nature of bound electron-hole pairs in this material class.