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 $s$- and $d$-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 $\mu$ between zero- 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 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 $\mu$ if the $s$-channel interaction is mixed sufficiently, the d-wave superconductivity has the advantage of achieving a high $T_{c}$ over the s-wave one, once it occurs. 
Katsuji Sakai, Yasushi Yokoya and Yoshiko Oi Nakamura (Science Univ.   of Tokyo)