Manipulating spin-polarized photocurrents in 2D transition metal dichalcogenides

Significance Monolayer group VI transition metal dichalcogenides (TMDs) feature a massive Dirac fermion system with strong spin–valley locking. It provides a route to manipulate quantum states via the interplay of spin and valley degrees of freedom. Here we report that the spin polarization and spin–valley lifetime of free carriers are electrically detected via a spin–valve-like structure in monolayer TMDs. The long spin–valley lifetime (∼102 ns) of free carriers is electrically probed, contrasting to that of excitons (∼101–102 ps) probed by optical spectroscopy. It demonstrates the potential application of 2D TMDs in nonmagnetic semiconductor-based spintronics. Manipulating spin polarization of electrons in nonmagnetic semiconductors by means of electric fields or optical fields is an essential theme of the conceptual nonmagnetic semiconductor-based spintronics. Here we experimentally demonstrate an electric method of detecting spin polarization in monolayer transition metal dichalcogenides (TMDs) generated by circularly polarized optical pumping. The spin-polarized photocurrent is achieved through the valley-dependent optical selection rules and the spin–valley locking in monolayer WS2, and electrically detected by a lateral spin–valve structure with ferromagnetic contacts. The demonstrated long spin–valley lifetime, the unique valley-contrasted physics, and the spin–valley locking make monolayer WS2 an unprecedented candidate for semiconductor-based spintronics.