Measurable spin-polarized current in two-dimensional topological insulators

We propose a simple method for generating a spin-polarized current in a two-dimensional topological insulator. As z-component magnetic impurities exist on one edge of the Kane-Mele model, a subgap is opened in the corresponding pair of edge states, but another pair of gapless edge states is still protected by the time reversal symmetry. Thus the conductance plateau with the value e2/h in the subgap corresponds to a single-edge and spin-polarized current. We also find that the spin-polarized current is insensitive to weak non-magnetic disorder. This mechanism for generating spin-polarized currents is independent of the concrete theoretical model and can be generalized to two-dimensional topological insulators, such as HgTe/CdTe quantum wells and silicene nanoribbons.