d-Wave-Induced Josephson Current Counterflow in YBa2Cu3O7/Nb Zigzag 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 π facets in high-angle high- T_c grain boundaries. From the characteristics, we estimate a possible imaginary s-wave admixture to the order parameter of the YBa₂Cu₃O₇ to be below 1%.