Electron-phonon interaction for adiabatic anharmonic phonons

TL;DR

This paper investigates a Holstein-like electron-phonon model with anharmonic phonons, revealing phase transitions and phase separation phenomena using a combination of analytical and dynamical mean-field theory methods.

Contribution

It introduces a model with anharmonic phonons exhibiting phase transitions and relates it to correlated binary alloys, providing a qualitative phase diagram.

Findings

Identification of homogeneous, alternating, and disordered phases.

First order transition between homogeneous and alternating phases.

Second order transition between alternating and disordered phases.

Abstract

A model with Holstein-like electron-phonon coupling is studied in the limit of adiabatic phonons. The phonon distribution is anharmonic with two degenerate maxima. This model can be related to fermions in a correlated binary alloy and describes microscopic phase separation. We discuss the weak and strong electron-phonon coupling limit and present a qualitative phase diagram. In terms of the phononic displacements it consists of a homogeneous, an alternating, and a disordered phase. There is a first order phase transition between the homogeneous and the alternating phase, and second order phase transition between the alternating and the disordered phase. The opening of a gap inside the disordered phase is treated by a dynamical mean-field theory.