Anomalous spin signal and Josephson supercurrent in bulk-insulating topological insulators

Topological insulator materials have recently drawn a considerable interest due to their spin-helical surface band structure which ensures that a spin-polarization can be induced by an external charge current. In the first part of the talk, I will present how the spin- polarization can be detected by utilizing ferromagnetic tunnel contacts. We find that the spin signal follows theoretical prediction when the carrier density is high. In low carrier density samples, we observe an opposite sign of the spin signal which we demonstrate in terms of band bending and spin-polarized Rashba states. In the second part, I will discuss fabrication of Josephson junctions on similar topological insulator materials. We find that the junctions also show anomalous Fraunhofer pattern compared to 1/B (where B is the magnetic field) dependence in conventional Josephson junctions. We predict that the inhomogeneity of contact transparency may play a crucial role behind this anomalous observation.