Temperature- and quantum phonon effects on Holstein-Hubbard bipolarons

TL;DR

This paper investigates how temperature and quantum phonon effects influence bipolaron formation in the Holstein-Hubbard model, using advanced computational methods to analyze stability and dissociation under various conditions.

Contribution

It introduces an extension of quantum Monte Carlo and a variational approach to accurately study bipolaron behavior in the Holstein-Hubbard model at finite temperatures.

Findings

Thermal dissociation of intersite bipolarons occurs at high temperatures.

Electron-electron repulsion and phonon frequency significantly affect bipolaron stability.

Results relate bipolaron behavior to phenomena observed in manganites.

Abstract

The one-dimensional Holstein-Hubbard model with two electrons of opposite spin is studied using an extension of a recently developed quantum Monte Carlo method, and a very simple yet rewarding variational approach, both based on a canonically transformed Hamiltonian. The quantum Monte Carlo method yields very accurate results in the regime of small but finite phonon frequencies, characteristic of many strongly correlated materials such as, e.g., the cuprates and the manganites. The influence of electron-electron repulsion, phonon frequency and temperature on the bipolaron state is investigated. Thermal dissociation of the intersite bipolaron is observed at high temperatures, and its relation to an existing theory of the manganites is discussed.