Conductance spectroscopy of vertical topological Josephson junction Nb/(Bi0.5Sb0.5)2Te3/Nb

The surface states of a topological insulator (TI) can be induced with superconductivity through proximity with a conventional s-wave superconductor (S). To study the coupling between two superconducting TI surfaces, we report the growth and fabrication of vertical Josephson junctions with the topological insulators (Bi0.5Sb0.5)(2)Te-3 sandwiched between Nb electrodes. We observed two Josephson critical currents on the I-V characteristic at 3.5 K, attributed to the bulk Nb and the proximity-induced superconducting (Bi0.5Sb0.5)(2)Te-3 surfaces, respectively. The enhancement of conductance at these two critical currents leads to a bump and a plateau on the differential conductance spectroscopy. By further cooling down to 300 mK, a zero bias conductance peak (ZBCP) appears on the plateau, which is taken as a feature from the unconventional paring at the (Bi0.5Sb0.5)(2)Te-3-Nb interface.