Physics Colloquium: Topologically non-trivial superconducting systems

There has been great interest in novel materials demonstrating exotic quantum phases of matter, such as three-dimensional topological insulators. These materials are characterized by an insulating bulk surrounded by two-dimensional conducting surface states that are protected by time-reversal symmetry. Topological insulators can be transformed into exotic superconductors with unconventional pairing by either coupling them with s-wave superconductors or chemically doping them. The resulting systems host zero-energy quasiparticle excitations called Majorana bound states, which can robustly store quantum information and potentially revolutionize quantum computation. In the first part of my talk, I will discuss measurements of Josephson junctions with topological insulator weak links such as Bi₂Se₃. Investigations of such topological junctions in superconducting quantum interference devices (SQUIDs) reveal an anomalous supercurrent that is carried by low-energy surface bound states. In the second part, I will discuss our preliminary results on Andreev reflection spectroscopy of Nb doped Bi₂Se₃ in the context of p-wave pairing gap in superconducting doped topological insulators. The measurements point toward the realization of topological superconductivity and topological quantum computation.