Superconducting order parameter symmetry in multilayer cuprates.

In this paper we classify the allowed order parameter symmetries in multilayer cuprates and discuss their physical consequences, with emphasis on Josephson tunneling and impurity scattering. Our solutions to the gap equation are based on highly non-specific forms for the interand intra-plane pairing interactions in order to arrive at the most general conclusions. Within this framework, the bi-layer (N = 2) case is discussed in detail with reference to YBCO and BSCCO and the related Landau-Ginzburg free energy functional. Particular attention is paid to the role of small orthorhombic distortions as would derive from the chains in YBCO and from superlattice effects in BSCCO, which give rise to a rich and complex behavior of the multilayer order parameter. This order parameter has N components associated with each of the N bands or layers. Moreover, these components have specific phase relationships. In the orthorhombic bi-layer case the (s,−s) state is of special interest, since for a wide range of phase space, this state exhibits π phase shifts in corner Josephson junction experiments. In addition, its transition temperature is found to be insensitive to non-magnetic inter-plane disorder, as would be present at the rare earth site in YBCO, for example. Of particular interest, also, are the role of van Hove singularities which are seen to stabilize states with dx2−y2-like symmetry, (as well as nodeless s-states) and to elongate the gap functions along the four van Hove points, thereby leading to a substantial region of gaplessness. We find that dx2−y2-like states are general solutions for repulsive interactions; they possess the fewest number of nodes and therefore the highest transition temperatures. In this way, they should not be specifically associated with a spin fluctuation driven pairing mechanism. PACS numbers: 74.72.-h, 74.20.Mn, 74.50.+r, 74.62.-c Typeset using REVTEX 1 REVTEX 3.0 Levin Group Preprint, 1995