Josephson Tunneling between Superconducting Topological Surface States

Proximity at the interface of a 3D topological insulator (TI) and a conventional s-wave superconductor can induce a 2D topological superconducting state. We grew s-wave superconductor (Nb)/TI (Bi-Sb-Te)/s-wave superconductor(Nb) heterostructures using molecular beam epitaxy (MBE) and fabricated sandwich typed Josephson junctions. Through the superconducting proximity effect, we realized topological superconducting surface states on both the top and bottom surfaces of the topological insulator film. Transport measurements showed an anomalous zero-bias conductance peak (ZBCP) at 135mK, in addition to the conventional Josephson effect between the two superconductor leads. This suggests Josephson tunneling occurs between the two proximity-driven topological surface states.