Multivalley dynamics in monolayer TMDs at high pressures revealed by double-resonance Raman

Transition metal dichalcogenides (TMDs) possess unique spin-valley locked and spin-split K/K’ valleys which have led to many fascinating valley-related phenomena. Furthermore, TMDs also exhibit other conduction band minima with similar properties, the Q/Q’ valleys. Previous reports demonstrated exciting physical phenomena involving K-Q scattering, but those effects are usually hindered in monolayer TMDs because of the energy difference between K and Q valleys. To unlock new multivalley phenomena in monolayer TMDs, it is desirable to reduce that energy difference, while being able to sensitively probe the valley shifts and the multivalley scattering processes. Here, we compress monolayer MoS₂ and WSe₂ at high-pressures and probe K-Q crossing and multivalley scattering via double resonance Raman scattering for the first time. The ability to probe K-K’ and K-Q scattering processes as a function of strain shall shed light on different multivalley phenomena in TMDs such as superconductivity, intervalley quantum interference and valley transport.