Proximity-induced superconductivity in topological Bi2Te2Se and Bi2Se3 films: Robust zero-energy bound state possibly due to Majorana fermions

Point contact conductance measurements on topological Bi2Te2Se and Bi2Se3 films reveal a signature of superconductivity below 2-3 K. In particular, critical current dips and a robust zero-bias conductance peak are observed. The latter suggests the presence of zero-energy bound states that could be assigned to Majorana fermions in an unconventional topological superconductor. We attribute these observations to proximity-induced local superconductivity in the films by small amounts of superconducting Bi inclusions or segregation to the surface, and provide supportive evidence for these effects.