Excitonic valley polarization and coherence in few-layer MoS2

Abstract

We study the excitonic valley polarization and coherence in few-layer MoS2 by using circular- and linear-polarization-resolved photoluminescence. The valley polarization is largest in monolayer MoS2 and decreases with increasing number of layers or temperature. Contrary to the valley polarization, the linear polarization is negligibly small in monolayer MoS2 and increases with increasing number of layers or temperature. The temperature-dependent valley depolarization can be explained by the exciton center-of-mass momentum-dependent electron-hole exchange interaction. The valley decoherence in few-layer MoS2 is much faster than the valley depolarization at low temperature and is steady against increasing temperature or photoexcitation intensity, indicating that the decoherence process does not involve phonon or carrier-carrier scattering. The dominant valley decoherence has a pure dephasing origin and cannot be explained by the valley-depolarizing e-h exchange interaction.