Interplay between extended s-wave and d-wave superconductivity in the nonlinear field representation

We consider a Hubbard type Hamiltonian for a two-dimensional superconductin g plane with a tight-binding dispersion relation. In addition, the energy g ap is considered to be either an extended s-wave, a d-wave form or a combin ation of both. We then derive the resultant coupled field equations of moti on for the spin-up and spin-down fields. The equations are of a highly nonl inear character but are still tractable. The s-wave and d-wave regimes are treated separately. It is shown that the superposition of s- and d-wave com ponents results in the emergence of striped patterns of superconducting ord er parameter densities and of square and triangular order parameter distrib utions. (C) 1999 Published by Elsevier Science B.V. All rights reserved.