Valley polarization and intervalley scattering in monolayer MoS2

We probe the degree of circular polarization of the emitted photoluminescence from a single layer of MoS2 as a function of the circularly polarized photo-excitation energy. A Single layer of MoS2 has strong emission at around 1.9 eV associated with a direct transition at the K-point of the Brillouin zone. The circular polarization of the photoluminescence is very high for excitation near the bandgap and has a power-law decrease as the excitation energy increases. We identify phonon-assisted intervalley scattering as the primary spin relaxation mechanism and present a model that explains the wide variation in values for the polarization reported in the literature.