Hartree-Fock study of electronic ferroelectricity in the Falicov-Kimball model with $f$-$f$ hopping

TL;DR

This study uses Hartree-Fock approximation to explore electronic ferroelectricity in the Falicov-Kimball model with $f$-$f$ hopping, revealing its robustness across different dimensions and interaction strengths.

Contribution

It extends previous Hartree-Fock analyses to small hopping values, weak interactions, and three dimensions, confirming ferroelectricity's stability in these regimes.

Findings

Ferroelectricity persists at small $f$-electron hopping.

The phase diagram matches Monte Carlo results in 2D.

Ferroelectricity remains stable in 3D.

Abstract

The Hartree-Fock (HF) approximation with the charge-density-wave (CDW) instability is used to study the ground-state phase diagram of the spinless Falicov-Kimball model (FKM) extended by $f$-$f$ hopping in two and three dimensions. It is shown that the HF solutions with the CDW instability reproduce perfectly the two-dimensional intermediate coupling phase diagram of the FKM model with $f$-$f$ hopping calculated recently by constrained path Monte Carlo (CPMC) method. Using this fact we have extended our HF study on cases that have been not described by CPMC, and namely, (i) the case of small values of $f$-electron hopping integrals, (ii) the case of weak Coulomb interactions and (iii) the three-dimensional case. We have found that ferroelectricity remains robust with respect to the reducing strength of coupling ($f$-electron hopping) as well as with respect to the increasing dimension of the system.