Hybridized Excitons in WS₂/MoSe₂ Heterobilayers Visualized by Time- and Angle-Resolved Photoemission Spectroscopy

Heterostructures consisting of stacked, twisted bilayers of transition metal dichalcogenides (TMDs) are a unique platform to achieve tunable optoelectronic properties. The twist angle yields a moiré superlattice that spatially modulates the electronic band structure and leads to the formation of interlayer excitons, in which the electron and hole of the exciton occupy different TMD layers. In WS₂/MoSe₂ twisted bilayers, the conduction bands align nearly degenerately, leading to hybridization between intralayer and interlayer excitons. Here, we present the momentum-resolved ultrafast dynamics of hybrid exciton states in a near-60-degree twisted WS₂/MoSe₂ heterobilayer. Using time- and angle-resolved photoemission spectroscopy, we directly visualize the lifetimes and energetics of both intralayer and hybridized exciton states in momentum space. We also characterize the temperature- and exciton density-dependence of these dynamics, as well as the interplay of the formation of intervalley momentum-forbidden dark excitons. Our results provide important insights into the effects of the moiré superlattice and band alignment on the ultrafast exciton dynamics.