Phase Transitions in the Pseudospin-Electron Model

TL;DR

This review discusses phase transitions, thermodynamics, and instabilities in the pseudospin-electron model (PEM), emphasizing its applications to strongly correlated systems and high-temperature superconductors, using mean field and random phase approximations.

Contribution

It provides a comprehensive overview of phase transitions and instabilities in PEM, including new criteria for phase realization and comparisons with the Falicov-Kimball model.

Findings

Identification of conditions for phase transitions into various states

Analysis of structural and dielectric instabilities

Comparison of PEM thermodynamics with Falicov-Kimball model

Abstract

A review of the present state of investigations of the pseudospin-electron model (PEM), which is used in the theory of strongly correlated electron systems, is given. The model is used to describe the systems with the locally anharmonic elements of structure represented in the model by pseudospins. The consideration is based on the dynamical mean field theory approach and the generalized random phase approximation. Electron spectrum and thermodynamics of the model are investigated; the cases of the simplified model, the model with strong interaction and the two-sublattice model are studied more in detail. The phase transitions into other uniform or modulated states as well as superconducting phases are described; the criteria of their realization are established. Based on this, the description of structural and dielectric (ferroelectric type) instabilities, phase separation and bistability phenomena is given. A comparison is made with the thermodynamics of the Falicov-Kimball model (which can be considered as a particular case of PEM). The possibility of applying the PEM to the analysis of thermodynamics of the real HTSC systems is discussed. Attention is paid to the unsolved problems in the study of PEM.