Excitonic band topology in two-dimensional topological materials

In recent years, the interplay of topological and excitonic effects in low-dimensional materials has been under significant investigation, especially in relation to a topological excitonic condensate (TEC) state. However, it is still not clear how the single excitonic band topology is affected by the underlying conduction and valence band topology which ultimately leads to the TEC state. In this work, we study this interplay of excitonic and topological effects using the ab initio GW plus Bethe-Salpeter equation approach. We calculate excitonic band structure, excitonic Berry curvature, and phase symmetry of the lowest excitonic band of candidate TEC materials, including monolayer 1T’ MoS₂ monolayer, and bilayer InAs/GaSb. Our work provides interesting avenues to study topological excitonic effects in semiconductors/semi-metals and explains the possible origin of the TEC state in two-dimensional topological materials.