Phase transition between d-wave and anisotropic s-wave gaps in high temperature oxides superconductors

TL;DR

This paper models high-temperature superconductivity considering two interactions, revealing a phase transition from d-wave to anisotropic s-wave gaps influenced by doping levels and antiferromagnetic fluctuations.

Contribution

It introduces a model with two competing interactions, showing a first-order phase transition between d-wave and anisotropic s-wave gaps in high-Tc superconductors.

Findings

Weak BCS attraction can yield high Tc with van Hove anomaly

AF interactions are crucial for d-wave pairing

Gap symmetry transitions from s-wave to anisotropic s-wave with doping

Abstract

We study models for superconductivity with two interactions: $V^>$ due to antiferromagnetic(AF) fluctuations and $V^<$ due to phonons, in a weak coupling approach to the high temperature superconductivity. The nature of the two interactions are considerably different; $V^>$ is positive and sharply peaked at ($\pm\pi$,$ \pm\pi$) while $V^<$ is negative and peaked at ($0,0$) due to weak phonon screening. We numerically find (a) weak BCS attraction is enough to have high critical temperature if a van Hove anomaly is at work, (b) $V^>$ (AF) is important to give d-wave superconductivity, (c) the gap order parameter $\Delta({\bf k})$ is constant(s-wave) at extremely overdope region and it changes to anisotropic s-wave as doping is reduced, (d) there exists a first order phase transition between d-wave and anisotropic s-wave gaps. These results are qualitatively in agreement with preceding works; they should be modified in the strongly underdope region by the presence of antiferromagnetic fluctuations and ensuing AF pseudogap.