The phase diagram of an orthorhombic d-wave superconductor

Possible pure and mixed symmetry phases of the superconducting order parame ter are studied for a two dimensional system of orthorhombic symmetry which is assumed to be a representative of the CuO2 planes typical for high T-c superconductors. The anisotropy of the Fermi surface due to the orthorhombi city is described by an effective mass model The study is based on the BCS- theory of anisotropic superconductors and reveals that an (s + d)-symmetric order parameter is the stable solution for the biggest part of the availab le parameter space. A small packet in which an [s + i(s + d)]-symmetric ord er parameter is the stable solution has also been found. (C) 1999 Elsevier Science B.V. All rights reserved.