Optical determination of the relation between the electron-boson coupling function and the critical temperature in high T$_c$ cuprates

TL;DR

This study reconstructs the electron-boson coupling spectrum in high-Tc cuprates using optical conductivity data, revealing a consistent peak and continuum, and shows that electron-phonon interaction is unlikely the main pairing mechanism.

Contribution

It introduces a method to extract the glue function from optical conductivity in high-Tc cuprates and links the coupling spectrum to the critical temperature across doping levels.

Findings

Robust peak at 50-60 meV in the glue spectrum.

Correlation between glue spectrum and critical temperature.

Electron-phonon coupling is excluded as the primary pairing mechanism.

Abstract

We take advantage of the connection between the free carrier optical conductivity and the glue function in the normal state, to reconstruct from the infrared optical conductivity the glue-spectrum of ten different high-Tc cuprates revealing a robust peak in the 50-60 meV range and a broad con- tinuum at higher energies for all measured charge carrier concentrations and temperatures up to 290 K. We observe that the strong coupling formalism accounts fully for the known strong temperature dependence of the optical spectra of the high Tc cuprates, except for strongly underdoped samples. We observe a correlation between the doping trend of the experimental glue spectra and the critical temperature. The data obtained on the overdoped side of the phase diagram conclusively excludes the electron-phonon coupling as the main source of superconducting pairing.