Observation of the Holstein shift in high $T_c$ superconductors with thermal modulation reflectometry

TL;DR

This study employs thermal modulation reflectometry to detect subtle changes in optical conductivity of high-temperature superconductors, revealing the Holstein shift and providing insights into electron-phonon interactions.

Contribution

It demonstrates the effectiveness of thermal modulation reflectometry in measuring small optical changes and extracts the electron-phonon spectral function in high-$T_c$ superconductors.

Findings

Detected the Holstein shift in high-$T_c$ superconductors.

Successfully extracted the electron-phonon spectral function.

Model calculations agree with experimental spectra.

Abstract

We use the experimental technique of thermal modulation reflectometry to study the relatively small temperature dependence of the optical conductivity of superconductors. Due to a large cancellation of systematic errors, this technique is shown to a be very sensitive probe of small changes in reflectivity. We analyze thermal modulation reflection spectra of single crystals and epitaxially grown thin films of YBa$_2$Cu$_3$O$_{7-\delta}$ and obtain the ${\alpha_tr}^2F(\omega)$ function in the normal state, as well as the superconductivity induced changes in reflectivity. We present detailed model calculations, based on the Eliashberg-Migdal extension of the BCS model, which show good qualitative and quantitative agreement with the experimental spectra. VSGD.93.12.th