Twofold symmetry of proximity-induced superconductivity in Bi${}_2$Te${}_3$/Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$ heterostructures revealed by scanning tunneling microscopy

Abstract

We observe proximity-induced superconductivity in the \textit{in situ} prepared heterostructures constructed by topological insulator Bi${}_2$Te${}_3$ thin films and high-temperature cuprate superconductors Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$. The superconducting gap maximum is about 7.6 meV on the surface of Bi${}_2$Te${}_3$ thin 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 a clear evidence of a twofold symmetric superconducting gap with gap minima along one pair of the principal crystalline axes of Bi${}_2$Te${}_3$. This gap form is consistent with the ${\Delta }_{4y}$ notation of the topological superconductivity proposed in such systems. Our results provide fruitful information of the possible topological superconductivity induced by the proximity effect in high-temperature superconducting cuprates.

6 pages, 4 figures