Phase diagram and dynamic response functions of the Holstein-Hubbard model

TL;DR

This paper maps the phase diagram of the Holstein-Hubbard model at zero temperature, revealing three paramagnetic phases and analyzing their spectral properties using advanced numerical methods.

Contribution

It provides the first comprehensive phase diagram and dynamical response functions for the Holstein-Hubbard model at half filling and zero temperature.

Findings

Identified metallic, bipolaronic, and Mott insulating phases.

Analyzed spectral functions near metal-insulator transitions.

Used DMFT with Exact Diagonalization and NRG methods.

Abstract

We present the phase diagram and dynamical correlation functions for the Holstein-Hubbard model at half filling and at zero temperature. The calculations are based on the Dynamical Mean Field Theory. The effective impurity model is solved using Exact Diagonalization and the Numerical Renormalization Group. Excluding long-range order, we find three different paramagnetic phases, metallic, bipolaronic and Mott insulating, depending on the Hubbard interaction U and the electron-phonon coupling g. We present the behaviour of the one-electron spectral functions and phonon spectra close to the metal insulator transitions.