Intravalley scattering probed by excitation energy dependence of valley polarization in monolayer MoS2

Steady-state valley polarization caused by polarized photoexcitation at various excitation energies reveals intravalley scattering from B excitons to A excitons in a monolayer of MoS2. When the excitation energy of circularly polarized light is increased from near the level of excitation of the A exciton, the valley polarization detected in the A exciton decreases monotonously and is completely suppressed due to phonon-mediated scattering. However, excitation to levels greater than the B-exciton energy recovers the valley polarization in the A exciton. By considering the suppressed valley coherence and the sign of the valley polarization, together with the higher energy shift of the recovered peak polarization of B-exciton resonance, we find that the polarization recovery originates from the phonon-mediated intravalley scattering from B excitons to A excitons in the same valley.