Pure spin-valley currents induced by spin-valley-momentum locked states and perfect optical-switch in WSe2-encapsulated bilayer graphene

Abstract

We study spin-valley optical conductivity in WSe2 encapsulated bilayer graphene. The Hamiltonian are based on tight binding model and the optical conductivity is calculated using Kubo's formula. As a result, in the case of longitudinal conductivity, switching of charge conductivity occurs when electric field is greater than SOI, while the spin and valley conductivities vanish for all photon frequencies. The perfect electrical switch is predicted. In the case of transverse conductivity, when electric field is absent, only spin current occurs and spin-momentum locked states appears, due to quantum spin hall phase. The behavior of spin and valley transverse currents is perfectly the same as the case of semi metallic phase and it is also controllable by the photon frequency. When electric field is greater than SOI, spin current direction may be selectable to be parallel or opposite to the direction of valley current, by varying photon frequency. Interestingly, we also find that when electric gap is equal to SOI, spin-valley-momentum locked states are predicted for the transverse currents. Pure spin-valley currents are also predicted. Some electron species are selectable to transport. Our work reveals the potential of bilayer graphene for application of topological-based spin-valley optoelectronics.