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

TL;DR

This study maps the phase diagram of pairing symmetries in 2D strong-coupling superconductors using Eliashberg equations, revealing conditions for s- and d-wave states and their critical temperatures.

Contribution

It provides a detailed phase diagram of pairing symmetries in 2D superconductors considering mixed interactions and band-filling effects, highlighting the conditions for d-wave and s-wave superconductivity.

Findings

D-wave superconductivity appears above a threshold chemical potential.

S-wave can occur at any chemical potential with sufficient s-channel interaction.

D-wave can achieve higher critical temperatures than s-wave.

Abstract

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.