Low-energy kink in the nodal dispersion of copper-oxide superconductors: Insights from Dynamical Mean Field Theory

TL;DR

This study uses Dynamical Mean Field Theory to explore how electron-phonon interactions cause kinks in the electronic dispersion of copper-oxide superconductors, revealing effects of strong correlations and doping on kink characteristics.

Contribution

It demonstrates how strong electronic correlations and antiferromagnetic order influence the appearance and position of dispersion kinks in a Hubbard model with electron-phonon coupling.

Findings

Kinks appear only at large electron-phonon coupling or doping.

Kink position can exceed the renormalized phonon frequency.

Antiferromagnetic correlations enhance the electron-phonon effect.

Abstract

Motivated by the observation in copper-oxide high-temperature superconductors, we investigate the appearance of kinks in the electronic dispersion due to coupling to phonons for a system with strong electronic repulsion. We study a Hubbard model supplemented by an electron-phonon coupling of Holstein type within Dynamical Mean Field Theory (DMFT) utilizing Numerical Renormalization Group as impurity solver. Paramagnetic DMFT solutions in the presence of large repulsion show a kink only for large values of the electron-phonon coupling $\lambda$ or large doping and, contrary to the conventional electron-phonon theory, the position of such a kink can be shifted to energies larger than the renormalized phonon frequency $\omega_0^r$. When including antiferromagnetic correlations we find a stronger effect of the electron-phonon interaction on the electronic dispersion due to a cooperative effect and a visible kink at $\omega_0^r$, even for smaller $\lambda$. Our results provide a scenario of a kink position increasing with doping, which could be related to recent photoemission experiments on Bi-based cuprates.