Generation and transport of valley-polarized current in transition-metal dichalcogenides

In two-dimensional crystals of transition-metal dichalcogenides (TMDC) having strong spin-orbit interaction such as monolayer ${\mathrm{WSe}}_{2}$, quantum states can be labeled by a valley index $\ensuremath{\tau}$ defined in the reciprocal space and the spin index $s$. We developed a first-principles theoretical formalism to both qualitatively and quantitatively predict nonequilibrium quantum transport of valley-polarized currents. We propose a ${\mathrm{WSe}}_{2}$ TMDC transistor to selectively deliver net valley- and spin-polarized current ${I}_{\ensuremath{\tau},s}$ to the source or drain by circularly polarized light under external bias. Due to the lack of translational symmetry of the real-space device, we predict a depolarization effect that increases with the decrease of the channel length of the transistor.