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

We propose a way to measure the interference associated with two superconductors with a [ital d][sub [ital x]][sup 2][minus][ital y][sup 2] symmetry coupled by a Josephson weak link. An experimental realization shows no interference effects in a superconducting YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] film. The results are consistent with [ital s]-wave symmetry.