Interplay between topological insulators and superconductors

Topological insulators are insulating in the bulk but possess metallic surface states protected by time-reversal symmetry. Here, we report on a detailed electronic transport study in high-quality Bi ₂Se ₃ topological insulator thin films contacted by superconducting (In, Al, and W) electrodes. The resistance of the film shows an abrupt and significant upturn when the electrodes become superconducting. In turn, the Bi ₂Se ₃ film greatly weakens the superconductivity of the electrodes, significantly reducing both their transition temperatures and their critical fields. A possible interpretation of these results is that the superconducting electrodes are accessing the surface states and the experimental results are consequences of the interplay between the Cooper pairs of the electrodes and the spin-polarized current of the surface states in Bi ₂Se ₃.