Identification of Exciton Complexes in Charge-Tunable Janus WSeS Monolayers

Janus transition-metal dichalcogenide monolayers are artificial materials, where one plane of chalcogen atoms is replaced by chalcogen atoms of a different type. Theory predicts an in-built out-of-plane electric field, giving rise to long-lived, dipolar excitons, while preserving direct-band g a p optical tran-sitions in a uniform potential landscape. Previous Janus studies had broad photoluminescence (>18 meV) spectra obfusca t i n g their specific excitonic origin. Here, we identif y the neutral and the negatively charged inter-and intravalley exciton transitions in Janus WSe S monolayers with similar to 6 meV optical line widths. We integrate Janus monolayers into vertical heterostructures, allowing doping control . Magneto-optic measurements indicate that monolayer WSe S has a direct bandgap at the K points. Our results pave the way for applications such as nanoscale sensing, which relies on resolv i n g excitonic energy shifts, and the development of Janus-based optoelectronic devices, which requires charge-state control and integration into vertical heterostructures.