Interplay and competition between superconductivity and charge orderings in the zero-bandwidth limit of the extended Hubbard model with pair hopping and on-site attraction

TL;DR

This paper investigates a generalized local pair superconductor model, analyzing how superconductivity and charge orderings compete or coexist, revealing phase diagrams with multiple homogeneous and phase-separated states.

Contribution

It extends the standard local pair superconductor model to include finite pair binding energy and intersite interactions, providing a detailed mean-field phase diagram analysis.

Findings

Identification of superconducting, charge-ordered, and non-ordered phases.

Existence of phase separation between superconducting and charge-ordered states.

Dependence of phase stability on interaction parameters.

Abstract

We present studies of an effective model which is a simple generalization of the standard model of a local pair superconductor with on-site pairing (i.e., the model of hard core bosons on a lattice) to the case of finite pair binding energy. The tight binding Hamiltonian consists of (i) the effective on-site interaction U, (ii) the intersite density-density interactions W between nearest-neighbours, and (iii) 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. Our investigations of the U<0 and W>0 case show that, depending on the values of interaction parameters, the system can exhibit three homogeneous phases: superconducting (SS), charge-ordered (CO) and nonordered (NO) as well as the phase separated SS-CO state.