Order-parameter symmetries in high-temperature superconductors

We present two representations of the order-parameter (OP) eigenfunctions for tetragonal cuprate superconductors, and for orthorhombic YBa₂Cu₃O_7-δ and Bi₂Sr₂CaCu₂O_8+δ (BSCCO). Recent BSCCO c-axis twist Josephson junction experiments of Li et al. demonstrate that the tunneling is strongly incoherent, and that the OP contains an isotropic s-wave component, but not any d_x²-y²-wave component. We propose a c-axis twist tetracrystal ring experiment.