Twofold symmetry of proximity-induced superconductivity in Bi2Te3/ Bi2Sr2CaCu2O8+δ heterostructures revealed by scanning tunneling microscopy

We observe proximity-induced superconductivity in in situ prepared heterostructures constructed by topological insulator Bi2Te3thin films and high-temperature cuprate superconductors Bi2Sr2CaCu2O8+δ. The superconducting gap maximum is about 7.6 meV on the surface of Bi2Te3thin films with a thickness of two quintuple layers, and the gap value decreases with an increase in the film thickness. Moreover, the quasiparticle interference data show clear evidence of a twofold symmetric superconducting gap with gap minima along one pair of the principal crystalline axes of Bi2Te3. This gap form is consistent with the Δ4y notation of the topological superconductivity proposed in such systems. Our results provide fruitful information on the possible topological superconductivity induced by the proximity effect in high-temperature superconducting cuprates.