Nature of Emergent Moiré Excitations in MoSe(2)/WS(2) Moiré Superlattices.

Moiré superlattices of semiconducting transition-metal dichalcogenide (TMD) heterobilayers are model systems for investigating strongly correlated electronic and excitonic phenomena. MoSe/WS moiré superlattices, which have a type-I band alignment, host fascinating correlated excitonic states. Although new moiré excitons in MoSe/WS have been widely reported, their microscopic origin has remained unclear. Here, combining large-scale first-principles calculations and microreflection spectroscopy, we identify the nature of these excitons. Our results show that excitonic resonances around MoSe A exciton energy are mainly determined by periodic strain patterns arising from atomic reconstruction of the TMD layers rather than interlayer hybridization, which had been the most common explanation previously. Consistently, no interlayer dipole can be observed in the vertical electric-field dependence of the moiré exciton resonance. Our results provide a microscopic explanation for the formation of moiré excitons in MoSe/WS moiré superlattices and highlight the important role of structural reconstructions in general TMD moiré superlattices.