Intermediate Coupling Theory of Electronic Ferroelectricity

TL;DR

This paper investigates the quantum phase diagram of an extended Falicov-Kimball model in intermediate coupling, revealing exciton Bose-Einstein condensation with electric polarization, and explores how hybridization affects ferroelectricity.

Contribution

It provides the first detailed quantum phase diagram of the model in this regime using Monte Carlo methods, highlighting the role of exciton condensation and hybridization in ferroelectricity.

Findings

Bose-Einstein condensation of excitons dominates the phase diagram.

Finite hybridization removes the condensate but enhances ferroelectricity.

Analytical features are complemented by Monte Carlo calculations.

Abstract

We calculate the quantum phase diagram of an extended Falicov-Kimball model for one and two-dimensional systems in the intermediate coupling regime. Even though some features of the phase diagram are obtained analytically, the main results are calculated with a constrained path Monte Carlo technique. We find that this regime is dominated by a Bose-Einstein condensation of excitons with a built-in electric polarization. The inclusion of a finite hybridization between the bands removes the condensate but reinforces the ferroelectricity.