Metastability and phase separation in a simple model of a superconductor with extremely short coherence length

TL;DR

This paper investigates a simplified superconductor model highlighting metastability and phase separation, revealing tricritical points and first-order transitions between metastable phases using mean-field analysis.

Contribution

It introduces a study of metastable phases and phase separation in a simple superconductor model with short coherence length, focusing on metastability and tricritical behavior.

Findings

Metastable superconducting and nonordered phases coexist within phase-separated regions.

A first-order transition occurs between metastable phases.

The model exhibits tricritical points in the phase diagram.

Abstract

We present studies of the atomic limit of the extended Hubbard model with pair hopping for arbitrary electron density and arbitrary chemical potential. The Hamiltonian consists of (i) the effective on-site interaction $U$ and (ii) the intersite charge exchange term $I$, determining the hopping of electron pairs between nearest-neighbour sites. In the analysis of the phase diagrams and thermodynamic properties of this model we treat the intersite interactions within the mean-field approximation. In this report we focus on metastable phases and determine their ranges of occurrence. Our investigations in the absence of the external magnetic field show that the system analysed exhibits tricritical behaviour. Two metastable phases (superconducting and nonordered) can exist inside the regions of the phase separated state stability and a first-order transition occurs between these metastable phases.