  Two dimensional (2D) materials provide a unique platform for spintronics and
valleytronics due to the ability to combine vastly different functionalities
into one vertically-stacked heterostructure, where the strengths of each of the
constituent materials can compensate for the weaknesses of the others. Graphene
has been demonstrated to be an exceptional material for spin transport at room
temperature, however it lacks a coupling of the spin and optical degrees of
freedom. In contrast, spin/valley polarization can be efficiently generated in
monolayer transition metal dichalcogenides (TMD) such as MoS2 via absorption of
circularly-polarized photons, but lateral spin or valley transport has not been
realized at room temperature. In this letter, we fabricate monolayer
MoS2/few-layer graphene hybrid spin valves and demonstrate, for the first time,
the opto-valleytronic spin injection across a TMD/graphene interface. We
observe that the magnitude and direction of spin polarization is controlled by
both helicity and photon energy. In addition, Hanle spin precession
measurements confirm optical spin injection, spin transport, and electrical
detection up to room temperature. Finally, analysis by a one-dimensional
drift-diffusion model quantifies the optically injected spin current and the
spin transport parameters. Our results demonstrate a 2D spintronic/valleytronic
system that achieves optical spin injection and lateral spin transport at room
temperature in a single device, which paves the way for multifunctional 2D
spintronic devices for memory and logic applications.
