Comparison of the superconducting transition properties of YBa2Cu3O7 nanobridges with and without a twin boundary

We have fabricated nanobridges from YBa2Cu3O7 films deposited on LaAlO3 substrates by using a focused ion beam technique and studied their superconducting transition properties with and without a twin boundary (TB) crossing the bridge. The nanobridge dimensions were 200–500 nm in width and length, and 100 nm in thickness. All the nanobridges studied with or without a TB had a superconducting transition temperature Tc of 90 K with a zero-resistance transition at 86.5 K and high critical current density of ∼1 × 107 A/cm2 at 77 K. However, the current-voltage curves for the nanobridges with a TB showed Josephson tunneling characteristics near the transition, which is in clear contrast to the flux-flow-type transition behavior of those without a TB. According to a crystallographic analysis with d-wave symmetry of YBCO, the small mismatch angle of the TB itself was not sufficient to cause the Josephson effect. Secondary effects, such as stress and strain, are believed to be the origin.