Abstract

Topological insulators (TIs) are characterized by topologically protected surface states at a vacuum interface of a TI. Similar interface states are expected at the interface between a TI and any topologically trivial material. I will discuss recent work showing that the interface states at the boundary between a topologically-trivial semiconductor (SE) and a TI are controlled by the symmetry of the interface. In contrast to the well-studied helical Dirac surface states, SE-TI interface states exhibit elliptical contours of constant energy and complex spin textures with broken helicity. We derive a general effective Hamiltonian for SE-TI junctions, and propose experimental signatures such as an out of plane spin accumulation under a transport current and the opening of a spectral gap that depends on the direction of an applied in-plane magnetic field.