Stability of ultrasmooth surface morphology of (110) YBa2Cu3O7−δ homoepitaxial films and Nb/Au/(110) YBa2Cu3O7−δ junctions

Abstract

We report on ultrasmooth surface morphology and chemical activeness of (110)-oriented YBa2Cu3O7−δ (YBCO) films grown on (110) YBCO single-crystal substrates by scanning electron microscopy, reflection high-energy electron diffraction, and transmission electron microscopy observations. The stable (110) YBCO interface can be formed by in situ deposited thin Au film against the chemically active elements like Nb. The in situ formed Nb/Au/(110)YBCO junction shows clear two superconducting transitions Tc1=91.8 K and Tc2=8.20 K associated with YBCO and Nb films and large supercurrent (at least larger than 2.0×102 A/cm2) much more than expected phenomenological arguments of s wave and dx2−y2 wave.