Mott scattering at the interface between a metal and a topological insulator

We compute the spin-active scattering matrix and the local spectrum at the interface between a metal and a three-dimensional topological band insulator. We show that there exists a critical incident angle at which complete (100%) spin-flip reflection occurs and the spin-rotation angle jumps by pi. We discuss the origin of this phenomena, and systematically study the dependence of spin-flip and spin-conserving scattering amplitudes on the interface transparency and metal Fermi-surface parameters. The interface spectrum contains a well-defined Dirac cone in the tunneling limit and smoothly evolves into a continuum of metal-induced gap states for good contacts. We also investigate the complex band structure of Bi2Se3.