Optospintronics in graphene via proximity coupling

Observation of micron size spin relaxation lengths makes graphene an ideal material for spintronics applications. However, spin dependent scattering at the contact/graphene interfaces causes low spin injection efficiencies. An attractive solution would be employing optical spin injection schemes but the tiny spin orbit coupling and low optical absorption of graphene is a hurdle.
In this talk, we will discuss our attempts on optical spin injection into graphene by utilizing monolayer WSe₂’s spin-coupled valley-selective absorption property. Towards this, we fabricate heterostructure devices consisting of monolayer WSe₂, monolayer graphene and three layers of h-BN. A circularly polarized light is applied to selectively populate one of the valleys in the WSe₂ layer. This produces spin polarized excitons consisting of holes and electrons. The latter diffuses into the graphene layer and causes spin accumulation. This spin accumulation is detected by using h-BN tunnel barrier/Co electrodes. We exclude any spurious effects by prudently studying the separation, power intensity and incident light polarization dependences on the non-local signal. We also compare the non-local signals generated by the monolayer and bilayer WSe₂ to prove its valleytronic origin.