Moiré-controllable exciton localization and dynamics through spatially-modulated inter- and intralayer excitons in a MoSe2/WS2 heterobilayer

Moiré heterobilayers exhibiting spatially varying exciton localization that can be precisely controlled through the twist angle have emerged as exciting platforms for studying complex quantum phenomena. Here, we study the exciton landscape in MoSe2/WS2 heterobilayers through synergistic first-principles GW plus Bethe Salpeter equation (GW-BSE) calculations and complementary time- and angle-resolved photoemission spectroscopy (tr-ARPES). We find that the MoSe2/WS2 heterobilayer has a type I band alignment at large twist angles. In contrast, at small twist angles, there exist simultaneous spatially modulated regions of local type I band alignment, hosting bright intralayer excitons, and local type II band alignment, hosting long-lived interlayer excitons, due to lattice reconstruction in different high-symmetry regions. In tr-ARPES this manifests in the observation of long-lived excitons with electron population in only MoSe2 at large twist angles, while in samples with small twist angles, signals from two distinct long-lived exciton states with electron population in both layers are observed. Contrary to earlier studies, we find no excitonic hybridization near the low-energy absorption peaks in MoSe2/WS2, whose splitting can, instead, be explained by the lattice reconstruction. Here, the authors reveal how twisting MoSe2/WS2 layers controls exciton behaviour. Combining theory and ultrafast spectroscopy, they show that lattice reconstruction creates distinct bright and long-lived excitons without hybridization effects.