E ects of grain boundaries on the critical current of high - Tc superconductorsHubert

We study the temperature dependence of the Josephson critical current for diierent symmetries of the superconducting state. We generalize Zaitsev's model for a smooth interface to include diiuse scattering of quasiparticles at the boundary. For d-wave symmetry, we nd strong deviations from the Ambegaokar-Baratoo (AB) formula for SIS junctions. Similar results are obtained for s-wave superconductors provided one assumes large pair-breaking eeects at the interface (inelastic scattering, magnetic scattering, etc.). Our numerical calculations are able to explain experimental data measured on single grain boundary junctions as well as c-axis oriented granular lms of high-temperature superconductors (HTSC).