Imaging of pure spin-valley diffusion current in WS-WSe heterostructures.

Transition metal dichalcogenide (TMDC) materials are promising for spintronic and valleytronic applications because valley-polarized excitations can be generated and manipulated with circularly polarized photons and the valley and spin degrees of freedom are locked by strong spin-orbital interactions. In this study we demonstrate efficient generation of a pure and locked spin-valley diffusion current in tungsten disulfide (WS)-tungsten diselenide (WSe) heterostructures without any driving electric field. We imaged the propagation of valley current in real time and space by pump-probe spectroscopy.