Direct Observation of Room‐Temperature Intravalley Coherent Coupling Processes in Monolayer MoS2

Comprehensive understanding of the interactions between excited states with spin‐valley polarizations is crucial for the applications of monolayer 2D transition metal dichalcogenides (TMDs) in spin‐valleytronics. Here, by broadband femtosecond transient absorption spectroscopy with circularly polarized pump/probe lights, a systematic investigation on the many‐body interactions of band‐edge valley excitons in monolayer MoS2 is performed, where intravalley coherent coupling processes are directly observed at room temperature. Namely, when the intravalley mixing states in the superposition region of A‐exciton and B‐exciton states are excited, there is an intravalley coherent coupling between A‐exciton and B‐exciton in K valley (or A′‐exciton and B′‐exciton in K′ valley) with an oscillation frequency of ≈7–8 THz, rather than the intervalley excitonic coupling in general. The findings elucidate intravalley mixing and coherent oscillations in valley excitons of monolayer TMDs at room temperature, which can give insight into the many‐body coupling mechanisms of excited valley excitons in 2D TMDs.