Enhanced carrier binding and bond correlations in the Hubbard-Su-Schrieffer-Heeger model with dispersive optical phonons

TL;DR

This study investigates how dispersive optical phonons influence electron pairing and bond correlations in a one-dimensional Hubbard-SSH model, revealing enhanced singlet binding but not increased superconductivity, emphasizing the importance of phonon dispersion in realistic models.

Contribution

It demonstrates the effects of dispersive phonons on electron pairing and correlations in the Hubbard-SSH model, extending previous work beyond the Einstein phonon approximation.

Findings

Phonon dispersion significantly enhances singlet binding.

Enhanced binding does not lead to stronger superconducting correlations.

Robust bond correlations are observed due to phonon dispersion.

Abstract

Electron-phonon (e-ph) interactions play a crucial role in determining many properties of materials. In this context, the Su-Schrieffer-Heeger (SSH) model, where atomic motion modulates the electronic hopping, has gained significant attention due to its potential for strong electron pairing in relation to high-Tc superconductivity. Previous studies of the SSH models have addressed many aspects of this problem, but have focused heavily on either dilute or half-filled models with dispersionless (Einstein) phonons. Here, we study the effects of dispersive optical phonons on the lightly doped one-dimensional optical Hubbard-SSH model using the density matrix renormalization group. We observe a significant enhancement in singlet binding driven by phonon dispersion; however, by calculating various correlation functions, we find that the enhanced binding does not translate to increased superconducting correlations but rather robust bond correlations in the studied parameter regime. Nevertheless, the significant impact of phonon dispersion on these correlations highlights the need to go beyond the Einstein phonon limit while modeling realistic quantum materials.