Symmetrical high-T c superconducting bicrystal Josephson junctions: Dependence of the electrical properties on the misorientation angle

The electrical properties of junctions at symmetrical bicrystal boundaries in high-T _c superconducting films are studied as functions of the misorientation angle in the range 8°–45°. The junctions are prepared by growing YBa₂Cu₃O₇ (YBCO) epitaxial films on Y-ZrO₂ (YSZ) bicrystal substrates. The proportional relationship between the characteristic voltages and the normal conductivities of junctions is derived from the dependences of the critical current and the normal resistance on the misorientation angle. The results are interpreted within the model of a superconductor-dielectric with defect levels in the band gap of the superconductor. The deviations from the proportional relationship are explained by the junction inhomogeneity. The thickness of the effective dielectric layer in the bicrystal junction and the Bohr radius of electrons on the defects are estimated.