Phase diagram of the pairing symmetry in two-dimensional strong-coupling superconductors

Two-dimensional Eliashberg equations have been solved by use of a mixed interaction with sand d-channels. It is discussed what kind of pairing symmetry of the superconducting state can be realized when the channel mixing parameters and the band-filling are varied. By changing the mixing parameters and varying the chemical potential μ between zeroand 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 μ for the appearance of the d-wave superconductivity 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 μ if the s-channel interaction is mixed sufficiently, the d-wave superconductivity has the advantage of achieving a high Tc over the s-wave one, once it occurs.