Stable and metastable phases in the atomic limit of the extended Hubbard model with intersite density-density interactions

TL;DR

This study explores the phase diagram of an extended Hubbard model with intersite interactions, revealing complex critical behaviors and metastable phases using a variational mean-field approach.

Contribution

It provides a detailed analysis of metastable phases and transitions in an extended Hubbard model, including the effects of intersite interactions and electron concentration.

Findings

Existence of various critical points such as bicritical, tricritical, and critical-end points.

First- and second-order transitions between metastable phases.

Identification of metastable homogeneous phases within phase-separated regions.

Abstract

We have studied a simple effective model of charge ordered insulators. The tight binding Hamiltonian consists of the effective on-site interaction U and the intersite density-density interaction Wij (both: nearest-neighbor and next-nearest-neighbor). In the analysis of the phase diagrams and thermodynamic properties of this model we have adopted the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. Our investigations of the general case (as a function of the electron concentration) have shown that the system exhibits various critical behaviors including among others bicritical, tricritical, critical-end and isolated critical points. In this report we concentrate on the metastable phases and transitions between them. One finds that the first- and second order transitions between metastable phases can exist in the system. These transitions occur in the neighborhood of first as well as second order transitions between stable phases. For the case of on-site attraction the regions of metastable homogeneous phases occurrence inside the ranges of phase separated states stability have been also determined.