Charge Ordered Insulator without Magnetic Order Studied by Correlator Projection Method

TL;DR

This paper investigates the extended Hubbard model at quarter filling using the correlator projection method, revealing a charge ordered insulator without magnetic order at intermediate temperatures, contrasting with Hartree-Fock predictions.

Contribution

It introduces the correlator projection method for studying the extended Hubbard model and uncovers a charge ordered insulator lacking magnetic order, aligning with experimental observations.

Findings

Charge ordered insulator without magnetic order at intermediate temperatures

Suppressed magnetic order due to small exchange coupling J_eff

Results differ from Hartree-Fock approximation and match experiments

Abstract

The Hubbard model with additional intersite interaction `$V$' (the extended Hubbard model) is investigated by the correlator projection method (CPM). CPM is a newly developed numerical method which combines the equation-of-motion approach and the dynamical mean-field theory. Using this method, properties of the extended Hubbard Model at quarter filling are discussed with special emphasis on the metal-insulator transition induced by electron-electron correlations. The result shows a metal-insulator transition to a charge ordered insulator with antiferromagnetic order at low temperatures, but a charge ordered insulator without magnetic symmetry breaking at intermediate temperatures. Here, the magnetic order is found to be suppressed to low temperatures because of the smallness of the exchange coupling $J_{\rm eff}$. The present results are in sharp contrast with the Hatree-Fock approximation whereas in agreement with the experimental results on quarter-filled materials with strong correlations, such as organic conductors.