Repulsion and attraction in high Tc superconductors

TL;DR

This paper investigates how repulsive and attractive interactions influence the gap functions in high-Tc superconductors, proposing a systematic method to compute these functions and exploring conditions for high critical temperatures.

Contribution

It introduces a systematic method based on point group representations to compute gap functions and analyzes how interactions affect symmetry and critical temperature in high-Tc superconductors.

Findings

Pure s-wave superconductivity exists only at very low temperatures.

Attractive potentials on near shells expand gap functions and raise critical temperature.

Strong on-site repulsion shifts gap symmetry from A_{1g} to B_{1g}.

Abstract

The influence of repulsion and attraction in high-Tc superconductors to the gap functions is studied. A systematic method is proposed to compute the gap functions using the irreducible representations of the point group. It is found that a pure s-wave superconductivity exists only at very low temperatures, and attractive potentials on the near shells significantly expand the gap functions and increase significantly the critical temperature of superconductivity. A strong on-site repulsion drives the $A_{1g}$ gap into a $B_{1g}$ gap. It is expected that superconductivity with the $A_{1g}$ symmetry reaches a high critical temperature due to the cooperation of the on-site and the next-nearest neighbor attractions.