Superconducting proximity effect in topological insulator and superconductor hybrid structure has attracted intense attention in recent years in an effort to search for Majorana fermions in condensed matter systems. Here we report on the superconducting proximity effect in a ${\mathrm{Bi}}_2{\mathrm{Se}}_3/{\mathrm{NbSe}}_2$ junction fabricated with an all-dry transfer method. Experimentally measured differential conductance spectra exhibit a bias-independent conductance plateau (BICP) in the vicinity of zero bias below 7 K and a zero-bias conductance peak (ZBCP) appears below 2 K. We show that the BICP is due to the strong superconducting proximity effect between the superconductor and the topological surface states while the ZBCP is due to the bulk states of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. Our study gives direct evidence that the topological surface states can be strongly coupled to a superconductor and clarifies the different roles of surface states and bulk states in superconducting proximity effect.

• Received 26 July 2016

DOI:https://doi.org/10.1103/PhysRevB.96.075107