Valley Depolarization Dynamics in Monolayer Transition-Metal Dichalcogenides: Role of the Satellite Valley

The valley depolarization dynamics of free holes in monolayer transition-metal dichalcogenides are studied by solving the Boltzmann transport equation in real time fully ab inito. While monolayer MoSe2, WS2, WSe2, and MoTe2 possess long hole valley lifetimes due to the spin-valley locking effect, monolayer MoS2 unexpectedly shows ultrafast valley dynamics, with a hole valley lifetime two orders of magnitude shorter than those of the above four materials at room temperature. It is further revealed that the existence of the satellite Gamma valley in MoS2 provides an additional hole relaxation path where the Gamma valley acts as an intermediate in the hole relaxation between primary K' and K valleys, and moreover, the strong scattering between primary and satellite valleys ensures the ultrafast valley depolarization. By uncovering the pivotal role of the satellite valley, our results may have significant implications for finely controlling valley depolarization in the multivalley materials.