Two s-wave solutions for superconductivity in the extended Hubbard model

TL;DR

This paper discovers and analyzes a second s-wave superconducting solution in the extended Hubbard model, revealing complex phase behavior and potential first-order transitions, with implications for low-density electron pairs.

Contribution

It identifies and characterizes a second s-wave solution in the extended Hubbard model, expanding understanding of possible superconducting states.

Findings

Two s-wave solutions coexist in the extended Hubbard model.

First-order transitions between solutions are possible.

Phase diagram modifications are calculated.

Abstract

The existence of more than one solution for s-wave pairing in the extended Hubbard model is not often realized. This possibility was noted by Friedberg et al. [Phys. Rev B50, 10190 (1994)] in the case of two electrons on a lattice, without further analysis. In the present paper, the second solution is found also in the case of superconductivity of extended s-wave symmetry in the extended Hubbard model. The properties of both s-wave solutions are examined by mean-field methods and thresholds for their appearance are given. A possibility of the first-order transition is discovered and modifications of the phase diagram are calculated. Results of this paper in the limit of low electron density are also applicable to the bound, two-electron pairs.