Large room-temperature valley polarization by valley-selective switching of exciton ground state

We propose a theoretical scheme exploiting magnetic proximity effect to realize strong excitonic emission and large, nonvolatile valley polarization in monolayer ${\mathrm{MoS}}_{2}$ at room temperature. A moderate exchange field can lead to valley-selective switching of the exciton ground state from bright to dark and a large valley-exciton splitting at the same time. The duo work synergistically to achieve a temperature enhanced valley polarization: while a large valley splitting is the critical first step for creating a valley-exciton population imbalance, this imbalance is greatly enhanced by thermal excitation from the dark ground state, with orders of magnitude longer lifetime than that of the bright exciton. Realizing robust room-temperature emission and valley polarization is essential for controlling the valley degree of freedom for information processing.