All-optical injection of charge, spin, and valley currents in monolayer transition-metal dichalcogenides

Monolayer transition-metal dichalcogenides have recently become a playground for spintronics and valleytronics research. Their low-energy spectrum can be described by Dirac cones on the corners of Brillouin zone, but the physical properties are richer than those of graphene since the spin degeneracy is lifted and the optical selection rules are valley dependent. This has been exploited for the optical injection of spin-and valley-polarized currents by the application of static electric fields. In this paper we consider an all-optical method for the injection of charge-, spin-, and valley-polarized currents. The presence of both a fundamental optical field and its second harmonic can lead to the injection of currents due to a nonlinear effect involving the quantum interference between one-and two-photon absorption processes. We analyze how the injected quantities can be controlled through the parameters of the incident light fields, allowing capabilities of control beyond those achieved with static fields, and discuss the conditions for experimental verification of our results.