Strong electron-Boson coupling effect in the infrared spectra of $Tl_2 Ba_2 Ca Cu_2 O_{8+\delta}$

TL;DR

This study reveals strong electron-Boson coupling in the infrared spectra of Tl2Ba2CaCu2O8+δ, showing unique spectral features and analyzing the relationship between the superconducting gap and Boson mode energy.

Contribution

It provides new experimental evidence of electron-Boson coupling effects in a high-Tc cuprate with a higher energy scale than similar compounds.

Findings

Reflectance shows a knee at 650 cm^-1 below Tc

Reflectance ratio has a minimum at 1000 cm^-1

Boson mode energy tends to decrease with Tc

Abstract

We report on a study of the in-plane infrared response of a \TBCCO film with $T_c$=108 K. The fingerprint evidence for a strong electron-Boson coupling has been observed. The raw reflectance below T$_c$ exhibits a knee structure at around 650 \cm and the ratio of the reflectances below and above T$_c$ displays a pronounced minimum at around 1000 \cm. In particular, the features appear at higher energy scale than other bilayer cuprates with T$_c$ around 90-95 K. The gap amplitude and the Boson mode energy were extracted from the analysis of the bosonic spectral function. In comparison with several other optimally doped high-Tc cuprates, we find that the gap size scales with T$_c$, but Boson mode energy has a tendency to decrease.