Intrinsic d-wave effects in YBa2Cu3O7-delta grain boundary Josephson junctions

We have measured the angular dependence of the Josephson critical current density (J(C)) in c-axis tilt biepitaxial grain boundary YBa2Cu3O7-delta junctions. We observe for the first time intrinsic d-wave pairing symmetry effects manifested as an oscillatory dependence of J(C) on angle. This intrinsic effect is evident even though spontaneous currents, possibly induced by faceting or barrier impurities, are observed in the grain boundaries.