Symmetry of the superconducting order parameter in a YBa2Cu3O7-δ epitaxial films

We propose a way to measure the interference associated with two superconductors with a dx2-y2 symmetry coupled by a Josephson weak link. An experimental realization shows no interference effects in a superconducting YBa2Cu3O7-δ film. The results are consistent with s-wave symmetry. © 1994 The American Physical Society.