PHASE-DIAGRAM OF THE PAIRING SYMMETRY IN 2-DIMENSIONAL STRONG-COUPLING SUPERCONDUCTORS

Two-dimensional Eliashberg equations have been solved by use of a mixe d interaction with s- and d-channels. It is discussed what kind of pai ring symmetry of the superconducting state can be realized when the ch annel mixing parameters and the band-filling are varied, By changing t he mixing parameters and varying the chemical potential mu between zer o- and half-filling, the pairing symmetry is determined and summarized into a phase diagram of the symmetry, It is revealed that there is an effective threshold in mu for the appearance of the d-wave supercondu ctivity regardless of the strength of the d-channel interaction. It is also shown that, although the s-wave superconductivity can occur for any value of mu if the s-channel interaction is mixed sufficiently, th e d-wave superconductivity has the advantage of achieving a high-T-c o ver the s-wave one, once it occurs. (C) 1997 Elsevier Science B.V.