Silicene is a one-atom-thick two-dimensional crystal of silicon with a hexagonal latticestructure that is related to that of graphene but with atomic bonds that are buckled ratherthan flat. This buckling confers advantages on silicene over graphene, because it should, inprinciple, generate both a band gap and polarized spin-states that can be controlled witha perpendicular electric field. Here we use first-principles calculations to show thatfield-gated silicene possesses two gapped Dirac cones exhibiting nearly 100% spin-polarization,situated at the corners of the Brillouin zone. Using this fact, we propose a design fora silicene-based spin-filter that should enable the spin-polarization of an output current tobe switched electrically, without switching external magnetic fields. Our quantum transportcalculations indicate that the proposed designs will be highly efficient (nearly 100%spin-polarization) and robust against weak disorder and edge imperfections. We also proposea Y-shaped spin/valley separator that produces spin-polarized current at two outputterminals with opposite spins.
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