Multiple topological interface states in silicene

Silicene is a 2D topological insulator due to its fairly large spin-orbital interaction and features a buckled lattice structure that allows one to control the effective mass of Dirac electrons by a perpendicular electric field. We propose the use of a spatially alternative electric field to generate multiple topologically-protected interface states (TIS) in the bulk silicene. It is shown that when the valley-dependent electron mass (defining the Chern number of an insulating bulk silicene) changes its sign or discontinues due to spatial variation of the electric field, multiple TIS appear in the insulating bulk silicene. The TIS come from the K and K' valleys and sustain dissipationless valley or spin-valley-dependent currents, which are immune to both the valley-conservation and spin-observation scattering. It is also found that the coupling among TIS due to spatial electron tunneling excites the TIS, and whether there is an excitation gap or not depends on the even or odd TIS number. Our findings may shed light on manufacturing topological electron devices.