Anisotropic current induced in topological surface states due to spin-polarized tunneling from a ferromagnet

Abstract

In clean tunneling junctions (TJs), the momentum parallel to the barrier is conserved in the tunneling process. We predict that this phenomenon can be observed in a TJ between a ferromagnet (FM) and a topological insulator (TI). The FM possesses spin-polarized electron states, while the TI has spin-momentum locked electron states. The tunneling probability is determined by the spin-matrix element between these electron states and leads to the injection of electrons into the TI with finite momentum parallel to the topological surface state. Due to the spin polarization of the electrons in the FM, the resulting current in the TI is not isotropic. The magnitude of the current is calculated quantitatively in terms of the ferromagnetic polarization and should be experimentally detectable using only an electrical setup.