Photoemission spectra of many-polaron systems

TL;DR

This study investigates how polaron behavior changes with carrier density in a one-dimensional model, revealing polaron dissociation and metallic behavior at intermediate coupling, challenging single-polaron theories for certain materials.

Contribution

It introduces a combined quantum Monte Carlo and exact diagonalization approach to analyze many-polaron systems at various densities in the Holstein model.

Findings

Polaron dissociation occurs with increasing band filling at intermediate coupling.

Normal metallic behavior emerges due to polaron dissociation.

Single-polaron theories are inadequate for some polaronic materials.

Abstract

The cross over from low to high carrier densities in a many-polaron system is studied in the framework of the one-dimensional spinless Holstein model, using unbiased numerical methods. Combining a novel quantum Monte Carlo approach and exact diagonalization, accurate results for the single-particle spectrum and the electronic kinetic energy on fairly large systems are obtained. A detailed investigation of the quality of the Monte Carlo data is presented. In the physically most important adiabatic intermediate electron-phonon coupling regime, for which no analytical results are available, we observe a dissociation of polarons with increasing band filling, leading to normal metallic behavior, while for parameters favoring small polarons, no such density-driven changes occur. The present work points towards the inadequacy of single-polaron theories for a number of polaronic materials such as the manganites.