Proximity-effect-induced superconductivity in Bi$_2$Se$_3$ and Bi$_2$Te$_3$

In this talk I will present our experimental investigations on the proximity effect between conventional superconductors such as Sn, Pb and the strong spin-orbit coupling materials Bi$_2$Se$_3$ or Bi$_2$Te$_3$ [1-3]. Several types of hybrid devices were fabricated, and their electron transport properties were measured down to $\sim$10 milli-Kelvin temperatures. The results show that a superconducting phase can be easily induced in Bi$_2$Se$_3$ and Bi$_2$Te$_3$ single crystals by superconducting Pb electrodes that are deposited on the surface of the former. The induced superconducting phase can be regarded as a true superconducting phase, i.e., it has an energy gap of the order 0.1 meV, and carries a Josephson supercurrent over a distance as far as several microns. The conductance spectrum of the interface between the induced superconducting phase and the normal phase of Bi$_2$Se$_3$ or Bi$_2$Te$_3$ exhibits a zero-bias peak. Based on the induced superconducting phase, single Josephson junction devices and superconducting quantum interference devices (SQUIDs) were constructied, and their critical supercurrent were investigated as a function of applied magnetic flux. We will discuss the implication of the results in terms of the pairing symmetry of the induced superconducting phase.\\[4pt] [1] F. Yang, et al., Phys. Rev. B 85, 104508 (2012).\\[0pt] [2] F. M. Qu, et al., Scientific Reports 2, 339 (2012). \\[0pt] [3] F. Yang, et al., Phys. Rev. B 86, 134504 (2012).