Spin-Valley pumping and long electron spin transport in a transition metal dichalcogenide monolayer

Monolayers of transition metal dichalcogenides (TMD) are ideal semiconductor materials to control both spin and valley degrees of freedom either electrically or optically. Nevertheless, optical excitation mostly generates excitons species with inherently short lifetime and spin/valley relaxation time. In this presentation we will show that we can strongly polarize (up to 75%) the resident electrons in n-doped WSe₂ and WS₂ monolayers by using a circularly polarized continuous wave laser [1]. Then, using a spatially-resolved optical pump-probe experiment, we measure the lateral transport of spin/valley polarized electrons over very long distances (tens of micrometers) [2]. These results highlight the key role played by the spin-valley locking effect in TMD monolayers on the pumping efficiency and the polarized electron transport.