Pairing interactions and pairing mechanism in high temperature copper oxide superconductors

TL;DR

This paper investigates the role of electron-phonon interactions and polarons in high-temperature cuprate superconductors, providing experimental and theoretical evidence for their contribution to the pairing mechanism.

Contribution

It identifies specific phonon modes and quantifies the electron-phonon coupling strength, highlighting the importance of polarons and charge transfer fluctuations in superconductivity.

Findings

Polaron binding energy is about 1.0 eV in undoped cuprates.

Strong electron-phonon coupling at ~20 meV influences superconductivity.

High-temperature superconductivity involves electron-phonon coupling, polarons, and charge transfer fluctuations.

Abstract

The polaron binding energy E_{p} in undoped parent cuprates has been determined to be about 1.0 eV from the unconventional oxygen-isotope effect on the antiferromagnetic ordering temperature. The deduced value of E_{p} is in quantitative agreement with that estimated from independent optical data and that estimated theoretically from the measured dielectric constants. The substantial oxygen-isotope effect on the in-plane supercarrier mass observed in optimally doped cuprates suggests that polarons are bound into the Cooper pairs. We also identify the phonon modes that are strongly coupled to conduction electrons from the angle-resolved photoemission spectroscopy, tunneling spectra, and optical data. We consistently show that there is a very strong electron-phonon coupling feature at a phonon energy of about 20 meV along the antinodal direction and that this coupling becomes weaker towards the diagonal direction. We further show that high-temperature superconductivity in cuprates is caused by strong electron-phonon coupling, polaronic effect, and significant coupling with 2 eV Cu-O charge transfer fluctuation.