Role of bosonic modes in the mechanism of high temperature Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ superconductors using ultrafast optical techniques

TL;DR

This study investigates the role of bosonic modes in high-temperature superconductivity of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ using ultrafast optical techniques, revealing a dual-component mechanism involving a dominant pairing interaction and a secondary electron-phonon effect.

Contribution

It provides new insights into the electron-boson coupling and suggests a two-component mechanism for high-$T_{c}$ superconductivity, challenging purely phonon-based explanations.

Findings

Correlation between coupling constant $\lambda$ and $T_c$ in overdoped samples

$\lambda$ too small to account for high $T_c$ via McMillan analysis

Identification of a dominant pairing interaction plus a weaker electron-phonon component

Abstract

Using ultrafast optical techniques, we probe the hole-doping dependence of the electron-boson coupling constant $\lambda$ in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$. In the overdoped region, we observe a correlation between ($\lambda$) and the superconducting transition temperature $T_{c}$. Upon performing the McMillan analysis, however, we find that $\lambda$ is too small to explain the high $T_{c}$'s, and that the Coulomb pseudopotential $\mu^{\ast}$ is negative. Our analysis therefore reveals two components in the mechanism of high-$T_{c}$ superconductivity -- a dominant pre-existing pairing interaction, together with a weaker electron-phonon interaction that fine-tunes $T_{c}$.