Spin-valley and layer polarizations induced by topological phase transitions in bilayer silicene

Abstract

We study spin-valley transport property in a single barrier bilayer silicene junction, where the barrier is under topological phase and controllable by electric field, staggered exchange field and off-resonant circularly polarized light. The tight binding model is adopted to describe the Hamiltonian. The ballistic transport through a topological barrier is investigated using the standard Landauer's formalism. The topological phases in bilayer silicene may be classified by spin-valley Chern numbers which is twice that in monolayer silicene. It is found that the four species of electron, two valley and two spin degrees of freedom, may be perfectly filtered. Electron having zero Chern number may allow to tunnel through the barrier, while the others are completely suppressed. This perfect spin-valley filter is due directly to topological phase transitions when staggered exchange field or off-resonant circularly polarized light is applied into the barrier. The perfect switching of layer (or pseudospin) polarization is predicted, allowed to control 100% carrier flowing only in top (or bottom) layer by electric field. The perfect switching from 100% to −100% of spin and valley polarizations is also found due to topological phase transition in the barrier. The result is quite different form transport property in bilayer graphene which lacks spin-orbit interaction and is planar atomic structure. This work reveals the potential of bilayer silicene as a topological material for spin-valleytronics.