Fano effect in the $a-b$ plane of Nd$_{1.96}$Ce$_{0.04}$CuO$_{4+y}$: evidence of phonon interaction with a polaronic background

TL;DR

This study presents evidence of Fano antiresonances in Nd$_{1.96}$Ce$_{0.04}$CuO$_{4+y}$, linking phonon interactions with a polaronic background, revealing insights into electron-phonon coupling in high-Tc superconductors.

Contribution

It demonstrates the presence of Fano antiresonances in the $a-b$ plane of Nd$_{1.96}$Ce$_{0.04}$CuO$_{4+y}$ and identifies the polaron band as the electronic continuum causing the effect.

Findings

Fano antiresonances observed in four transverse optical $E_u$ phonons.

Electronic continuum responsible for Fano effect is the polaron band.

Temperature dependence of phonon frequencies supports polaron interaction.

Abstract

Reflectance measurements in properly selected samples of Nd$_{1.96}$Ce$_{0.04}$CuO$_{4+y}$ with different carrier concentrations provide a firm evidence of Fano antiresonances for the four transverse optical $E_u$ phonons in the $a-b$ plane. Fits performed without any previous subtraction of the electronic background, as well as the dependence on temperature of the renormalized phonon frequencies, show that the electronic continuum repsonsible for the Fano effect is the polaron band found in all parent compounds of high-T$_c$ superconductors.