Enhancement of the critical current across a YBCO thin-film grain boundary junction due to Abrikosov vortices

Abstract

We have investigated experimentally and theoretically the magnetic field dependence of the critical current I cJ across a thin-film 24° bicrystal YBCO grain boundary junction at 4.2 K in an increasing and decreasing magnetic field H a up to 4.5 T. The theoretical model, which is based on the Ginzburg–Landau equation, uses the D'yachenko approach to estimate the supercurrents flowing parallel to the grain boundary. The model shows that the presence of Abrikosov vortices near the grain boundary significantly enhances the grain boundary current and causes I cJ( H a) to become hysteretic. Incorporating the thin-film planar geometry and the random inhomogeneity of the Josephson coupling current density along the grain boundary into the model leads to good agreement with the experimental I cJ( H a) data.