Charge orderings and phase separations in the atomic limit of the extended Hubbard model with intersite density-density interactions

TL;DR

This paper investigates charge orderings and phase separations in an extended Hubbard model with intersite interactions, revealing complex phase diagrams including phase separated states using a variational mean-field approach.

Contribution

It introduces a variational method that accounts for phase separated states in the extended Hubbard model with intersite interactions, expanding beyond previous analyses.

Findings

Charge ordered and nonordered phases identified.

Phase separated states such as CO--NO and CO--CO observed.

System behavior depends on the sign and magnitude of intersite interactions.

Abstract

A simple effective model of charge ordered insulators is studied. The tight binding Hamiltonian consists of the effective on-site interaction U and the intersite density-density interactions Wij (both: nearest-neighbour and next-nearest-neighbour). In the analysis of the phase diagrams we have adopted the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. The phase separated states have not been taken into account in previous analyses. Our investigations of two cases of the on-site interaction: attraction (U/(-W_Q)=-10) and repulsion (U/(-W_Q)=1.1) show that, depending on the values of the next-nearest-neighbour attraction, the system can exhibit not only homogeneous phases: charge ordered (CO) and nonordered (NO), but also various phase separated states (CO--NO, CO--CO).