The Hubbard model with intersite interaction within the Composite Operator Method

TL;DR

This paper investigates the extended Hubbard model using the Composite Operator Method, revealing complex phase diagrams, charge ordering phenomena, and implications for materials like manganese compounds and cuprates.

Contribution

It introduces a self-consistent computation of the fermionic propagator within the 2-pole approximation for the extended Hubbard model, analyzing phase transitions and material properties.

Findings

Rich phase diagrams with multiple phase transitions.

Charge ordering driven by intersite Coulomb interactions.

Insights into the behavior of cuprates and manganese compounds.

Abstract

We study the one- and two- dimensional extended Hubbard model by means of the Composite Operator Method within the 2-pole approximation. The fermionic propagator is computed fully self-consistently as a function of temperature, filling and Coulomb interactions. The behaviors of the chemical potential (global indicator) and of the double occupancy and nearest-neighbor density- density correlator (local indicators) are analyzed in detail as primary sources of information regarding the instability of the paramagnetic (metal and insulator) phase towards charge ordering driven by the intersite Coulomb interaction. Very rich phase diagrams (multiple first and second order phase transitions, critical points, reentrant behavior) have been found and discussed with respect to both metal-insulator and charge ordering transitions: the connections with the experimental findings relative to some manganese compounds are analyzed. Moreover, the possibility of improving the capability of describing cuprates with respect to the simple Hubbard model is discussed through the analysis of the Fermi surface and density of states features. We also report about the specific heat behavior in presence of the intersite interaction and the appearance of crossing points.