Bound states, spin polarization, and currents due to magnetic line defects at topological insulator surfaces

We show that a magnetic line defect on the surface of a topological Insulator generically supports two branches of spin-polarized and current carrying one-dimensional bound states. The velocity, and hence spin texture, of each of those branches can be independently tuned by a magnetic field rotated in the plane of the surface. We compute the local spin-resolved density of states as well as the net spin polarization and current due to both bound and scattering states as a function of potential and magnetic components of the scattering potential, and show that it varies stepwise. This work lays the foundation for defect engineering of spin textures and macroscopic currents at topological insulator surfaces.