Moiré effect on the higher-energy excitonic states in WSe₂/WS₂ superlattice

Moiré superlattices in two-dimensional van der Waals heterostructures have recently emerged as a platform for tailoring electronic and optical properties at the nanoscale. Recent studies have shown that exciton states in moiré superlattice have highly exotic electron-hole correlation, including unusual charge distribution and distinctive momentum space selection rule. While most moiré exciton studies to date have focused on the lowest energy excitations, our study here extends the exploration to the higher energy excited-state excitons. We present a first-principles study on the electronic and optical properties of these higher energy excitons in WS₂/WSe₂ moiré heterostructure utilizing the GW plus Bethe-Salpeter equation (GW-BSE) calculation combined with the recently developed pristine unit-cell matrix projection (PUMP) method. We study the interplay between the moiré potential and the fine structure of the higher energy exciton wavefunctions, mostly focusing on the 2s exciton within the WSe₂ layer, and how such interplay changes the exciton binding energies and manifest new optical features in the absorption spectra.