Bosonic Spectral Function and The Electron-Phonon Interaction in HTSC Cuprates

TL;DR

This paper reviews experimental evidence and theoretical models indicating strong electron-phonon interactions in high-temperature cuprate superconductors, supporting an Eliashberg-like mechanism for d-wave pairing.

Contribution

It combines experimental data analysis with theoretical modeling to clarify the role of electron-phonon interactions and strong correlations in high-Tc cuprates.

Findings

Strong EPI with coupling constants 1-3 near optimal doping

Experimental evidence supports Eliashberg-like theory for HTSC cuprates

EPI contributes to pairing strength, residual Coulomb interactions trigger d-wave pairing

Abstract

In Part I we discuss accumulating experimental evidence related to the structure and origin of the bosonic spectral function in high-temperature superconducting (HTSC) cuprates at and near optimal doping. Some global properties of the spectral function, such as number and positions of peaks, are extracted by combining optics, neutron scattering, ARPES and tunnelling measurements. These methods give convincing evidence for strong electron-phonon interaction (EPI) with the coupling constant between 1-3 in cuprates near optimal doping. Here we clarify how these results are in favor of the Eliashberg-like theory for HTSC cuprates near optimal doping. In Part II we discuss some theoretical ingredients - such as strong EPI, strong correlations - which are necessary to explain the experimental results related to the mechanism of d-wave pairing in optimally doped cuprates. These comprise the Migdal-Eliashberg theory for EPI in strongly correlated systems which give rise to the forward scattering peak. The latter is further supported by the weakly screened Madelung interaction in the ionic-metallic structure of layered cuprates. In this approach EPI is responsible for the strength of pairing while the residual Coulomb interaction (by including spin fluctuations) triggers the d-wave pairing.