Single-particle spectral function of the Holstein-Hubbard bipolaron

TL;DR

This paper investigates the spectral properties of the Holstein-Hubbard bipolaron in one dimension using cluster perturbation theory and the Lanczos method, revealing detailed dispersion and spectral weight features.

Contribution

It introduces a novel approach combining cluster perturbation theory with Lanczos to study the bipolaron spectral function at continuous wave vectors.

Findings

Accurate bipolaron dispersion matches previous high-precision results.

Pronounced deviations from simple tight-binding models are observed.

Next-nearest-neighbor hopping processes significantly influence the dispersion.

Abstract

The one-electron spectral function of the Holstein-Hubbard bipolaron in one dimension is studied using cluster perturbation theory together with the Lanczos method. In contrast to other approaches, this allows one to calculate the spectrum at continuous wave vectors and thereby to study, for the first time, the dispersion and the spectral weight of quasiparticle features. The formation of polarons and bipolarons, and their manifestation in the spectral properties of the system, is studied for the cases of intermediate and large phonon frequencies, with and without Coulomb interaction. A good agreement is found with the most accurate calculations of the bipolaron dispersion available, over a large range of the electron-phonon coupling strength. Additionally, pronounced deviations of the bipolaron dispersion from a simple tight-binding band are found, which can be attributed to next-nearest-neighbor hopping processes.