d-Wave–Induced Josephson Current Counterflow inYBa2Cu3O7/NbZigzag Junctions

Well-defined zigzag-shaped ramp-type Josephson junctions between YBa2Cu3O7 and Nb have been studied. The magnetic field dependencies of the critical currents provide evidence for d-wave?induced alternations in the direction of the Josephson current between neighboring sides of the zigzag structure. The arrays present controllable model systems to study the influences of ? facets in high-angle high- Tc grain boundaries. From the characteristics, we estimate a possible imaginary s-wave admixture to the order parameter of the YBa2Cu3O7 to be below 1%.