Dynamics of valley polarized excitations in monolayer MoSe2 using transient spin-grating spectroscopy

We report on a transient spin-grating measurement on CVD-grown monolayer MoSe2. Two cross-polarized 1.5 eV short laser pulses interfere on the sample to generate a polarization grating. This selectively induces K and K' valley excitations, the populations of which vary sinusoidally across the surface. The decay of this valley polarization grating is studied through a diffracted probe beam. We find that the decay strongly depends on the initial population and exhibits a characteristic temperature dependence. These results provide important insights into the lifetime and mechanisms for inter-valley scattering as well as possible scattering to dark exciton states in monolayer transition metal dichalcogenides.