Effects of the electron-phonon coupling near and within the insulating Mott phase

TL;DR

This paper investigates how electron-phonon interactions influence the Mott transition and insulating phase in the Holstein-Hubbard model, revealing that increased coupling reduces the Mott gap and aligns with experimental findings.

Contribution

It provides an analytic expression for the spectral density in the Mott insulator considering electron-phonon effects, using a variational slave boson approach.

Findings

Electron-phonon coupling reduces the Mott gap.

Mean-field results agree with numerical techniques.

Analytic spectral density expression derived for the Mott insulator.

Abstract

The role of the electron-phonon interaction in the Holstein-Hubbard model is investigated in the metallic phase close to the Mott transition and in the insulating Mott phase. The model is studied by means of a variational slave boson technique. At half-filling, mean-field static quantities are in good agreement with the results obtained by numerical techniques. By taking into account gaussian fluctuations, an analytic expression of the spectral density is derived in the Mott insulating phase showing that an increase of the electron-phonon coupling leads to a sensitive reduction of the Mott gap through a reduced effective repulsion. The relation of the results with recent experimental observations in strongly correlated systems is discussed.