  We investigated the electronic structure of a silicene-like lattice with a
line defect under the consideration of spin-orbit coupling. In the bulk energy
gap, there are defect related bands corresponding to spin helical states
localized beside the defect line: spin-up electrons flow forward on one side
near to the line defect and move backward on the other side, and vice verse for
spin-down electrons. When the system is subjected to random distribution of
spin-flipping scatterers, electrons suffer much less spin-flipped scattering
when they transport along the line defect than in the bulk. An electric gate
above the line defect can tune the spin-flipped transmission, which makes the
line defect as a spin-controllable waveguide.
