ORTHORHOMBICALLY MIXED S-WAVE AND D(X)2(-Y)2-WAVE SUPERCONDUCTIVITY AND JOSEPHSON TUNNELING

The effect of orthorhombicity on Josephson tunneling in high-T-c, supe rconductors such as YBa2Cu3O7-delta is studied for both single crystal s and highly twinned crystals. It is shown that experiments on highly twinned crystals experimentally determine the symmetry of the supercon ducting twin boundaries (which can be either even or odd with respect to a reflection in the twinning plane). Conversely, Josephson experime nts on highly twinned crystals cannot experimentally determine whether the superconductivity is predominantly s wave or predominantly d wave . The direct experimental determination of the order-parameter symmetr y by Josephson tunneling in YBCO thus comes from the relatively few ex periments which have been carried out on untwinned single crystals.