Pairing in Cu-O Models: Clues of Joint Electron-Phonon and Electron-Electron Interactions

TL;DR

This paper investigates how electron-electron and electron-phonon interactions jointly influence pairing in Cu-O models, revealing that certain lattice vibrations can enhance electronic pairing in cuprate superconductors.

Contribution

It introduces a combined model of electron-electron and electron-phonon interactions in Cu-O systems and shows that specific phonon modes can promote pairing, contrary to traditional expectations.

Findings

Vibrations in the Cu-O plane can synergize with electronic pairing.

Half-breathing phonon modes are crucial for pairing enhancement.

Electronic spectrum considerations reveal phonon effects are more complex than standard Jahn-Teller predictions.

Abstract

We discuss a many-electron Hamiltonian with Hubbard-like repulsive interaction and linear coupling to the phonon branches, having the Cu-O plane of the superconducting cuprates as a paradigm. A canonical transformation extracts an effective two-body problem from the many-body theory. As a prototype system we study the $\cu$ cluster, which yields electronic pairing in the Hubbard model; moreover, a standard treatment of the Jahn-Teller effect predicts distortions that destroy electronic pairing. Remarkably, calculations that keep all the electronic spectrum into account show that vibrations are likely to be synergic with electronic pairing, if the coupling to half-breathing modes predominates, as experiments suggest.