Coupling superconductors to topological insulators

The recent discovery of the topological insulators sparked an enormous attention. The experimental investigation of topological insulators with surface sensitive spectroscopic techniques evidently exposed the helical Dirac fermions living at the surface of a bulk insulator. In transport experiments, intrinsic bulk conduction challenges the observation of the topological surface states. We have observed electrical transport through the surface states of Bi$_{2}$Te3 by utilizing the electrical field effect and by utilizing intrinsically transparant interfaces to metallic electrodes. Of particular interest is coupling topogical insulators to superconductors, where at the interface the elusive Majorana fermion is predicted to recide. We fabricated superconductor -- topological insulator -- superconductor Nb-Bi$_{2}$Te$_{3}$-Nb junctions and observed a supercurrent over a length scale of more than a micrometer. Shapiro steps appear under microwave irradiation. The supercurrent is found to be surprisingly robust in large magnetic fields.