Transport Measurements on Topological Insulators with Superconductor Electrodes*

Interplay between topological insulators (TIs) and superconductors (SCs) is interesting to study novel physics such as Majorana fermions. Here we report transport measurements on bulk TI interfaced with superconducting electrodes, including indium (In) and niobium (Nb). The TI crystals are high quality $Bi_2Te_3, Bi_2Se_3, Bi_2Te_2Se$ grown by the Bridgman method. Multiple superconducting transitions have been observed in $Bi_2Te_3$/In systems, possibly due to the superconducting alloys formed by In and Bi. Below the superconducting temperature of In (or Nb), the resistance of TI/Sc structure shows a pronounced upturn which may be a probe of spin-polarized surface states in TI and the interplay with SC.