Spin-Polarized Charge Separation in a Photoexcited Transition Metal Dichalcogenide Heterobilayer at Room Temperature

Transition metal dichalcogenide (TMDC) monolayers feature spin-valley locking for band-edge electrons/holes and valley specific optical excitation by circularly polarized light. A potential application of the spin-valley polarization is to provide an efficient mechanism for spin-selective interfacial photochemistry. Here, we study spin-polarized charge separation at room temperature in a MoSe2/WSe2 heterobilayer with macroscopic dimensions. Using time-resolved Faraday rotation, we show that resonant excitation of valley-specific exciton transition in WSe2 results in spin-polarized charge separation across the MoSe2/WSe2 interface with spin polarization persisting on the 10 ps time scale. From dynamic changes in Faraday rotation and its dependences on excitation density and sample temperature, we present possible mechanisms of spin depolarization. We discuss potential applications of TMDC monolayers and heterobilayers for spin-selective interfacial photochemistry and time limits on competitive dynamics.