Josephson tunneling in high-Tcsuperconductors

In this article a macroscopic invariance group describing the superconducting state of a twinned crystal is introduced and shown to provide a useful framework for the discussion of Josephson tunneling in twinned crystals. Josephson tunneling from time-reversal symmetry-breaking states is described and compared with that from time-reversal invariant states for both twinned and untwinned crystals and for both c-axis and basal-plane currents, in a model for orthorhombic Y-Ba-Cu-O. In addition, a ring geometry, which allows s-wave and ${\mathit{d}}_{{\mathit{x}}^2\mathrm{-}{\mathit{y}}^2}$-wave superconductivity in a tetragonal superconductor to be distinguished on the basis of symmetry arguments only, is proposed and analyzed. Finally, an appendix gives details of the experimental Josephson tunneling evidence for a superconducting state of orthorhombic ${\mathit{ux}}^2$+${\mathit{vy}}^2$ symmetry in Y-Ba-Cu-O. © 1996 The American Physical Society.