Enhanced dexter coupling and increased Rydberg exciton splitting in Janus WSSe: signatures of reduced dielectric screening

Abstract Janus WSSe transition metal dichalcogenides monolayer dissimilar top and bottom layer breaks the mirror symmetry, instigating an out-of-plane electric field. This work shows how the out-of-plane electric field impacts the valley physics of the neutral exciton, its complex, and its excited states. Laser excitation energy sweeping reveals the position of the excited 2s exciton and the B-exciton. The exciton binding energy difference between 1s exciton and 2s exciton in Janus WSSe is larger than both parents WSe 2 and WS 2 . When in resonance with the B-exciton, excitons are predominantly generated in the opposite valley indicating enhanced Dexter coupling. These results constitute a comprehensive polarization-resolved photoluminescence study of Janus WSSe at resonant excitation, confirming the expected presence of valley polarization and valley coherence of the exciton, its complex, and its excited states; unveiling stronger Dexter coupling in conjunction with a larger exciton binding energy attributed to reduced screening.