Interplay between charge and magnetic orderings in the zero-bandwidth limit of the extended Hubbard model for strong on-site repulsion

TL;DR

This paper investigates a simplified model of strongly interacting electrons on a lattice, revealing complex phase diagrams with multiple ordered phases and multicritical points, relevant for understanding charge and magnetic orderings in insulators.

Contribution

It introduces an effective model incorporating charge and magnetic interactions treated within mean-field approximation, highlighting multicritical behaviors and phase separation phenomena.

Findings

Identification of at least 9 distinct phases including charge and magnetic orderings.

Discovery of multicritical points such as bicritical, tricritical, tetracritical, and critical end points.

Complex phase diagrams with various phase separation types.

Abstract

A simple effective model of charge ordered and (or) magnetically ordered insulators is studied. The tight binding Hamiltonian analyzed consists of (i) the effective on-site interaction U, (ii) the intersite density-density interaction W and (iii) intersite magnetic exchange interaction Jz (or Jxy) between nearest-neighbors. The intersite interaction are treated within the mean-field approximation. One shows that the systems considered can exhibit very interesting multicritical behaviors, including among others bicritical, tricritical, tetracritical and critical end points. The analysis of the model has been performed for an arbitrary electron concentration as well as an arbitrary chemical potential in the limit of strong on-site repulsion. The phase diagrams obtained in such a case are shown to consist of at least 9 different states, including four homogenous phases: nonordered (NO), ferromagnetic (F), charge ordered (CO), ferrimagnetic (intermediate, I) and five types of phase separation: NO-NO, F-NO, F-F, CO-F, CO-I.