Symmetry of order-parameters in high-Tc layered superconductors

It is well known that the anisotropy and wave-vector dependence of the energy-gap function determine many important properties of a superconductor which are relevant for device applications. Apart from a weak dependence on the wave-vector k-> in the direction perpendicular to the reciprocal layer-plane of a high-Tc layered superconductor, it is shown that anisotropic superconducting order parameters for intra-layer pairing in the class of such materials with orthorhombic crystal structures, can have either pure s-wave like symmetry or mixed d-wave and anisotropic extended s-wave like symmetries in the reciprocal layer-plane. However, in such materials with tetragonal crystal structures, it is possible to have a pure s-wave like symmetry, which may be either isotropic or anisotropic in the layer k->-space, or a pure d-wave like symmetry, as far the k->-dependence in the reciprocal layer plane is concerned. In view of this, some suggestions for analysing experimental data will also be presented. (author)