THz electrodynamics of BaFe$_{1.91}$Ni$_{0.09}$As$_{2}$ film analyzed in the framework of multiband Eliashberg theory

TL;DR

This study investigates the terahertz electrodynamics of a BaFeNiAs superconductor film using a multiband Eliashberg model, revealing insights into its superconducting mechanisms and electromagnetic properties.

Contribution

It applies a three-band Eliashberg theory to analyze terahertz spectra of a Fe-based superconductor, linking spin fluctuations to superconducting properties.

Findings

Superfluid density and plasma frequency were characterized across temperatures.

The superconducting coupling is mediated by antiferromagnetic spin fluctuations.

The characteristic energy of spin fluctuations scales with the critical temperature.

Abstract

The temperature dependences of the plasma frequency, superfluid density and London penetration depth were determined from terahertz spectra of conductivity and dielectric permittivity of BaFe$_{1.91}$Ni$_{0.09}$As$_{2}$ film with critical temperature $T_c=19.6$~K. Part of experimental data were analyzed within a simple three-band Eliashberg model where the mechanism of superconducting coupling is mediated by antiferromagnetic spin fluctuations, whose characteristic energy $\Omega_{0}$ scales with $T_{c}$ according to the empirical law $\Omega_{0} = 4.65k_{B}T_{c}$, and with a total electron-boson coupling strength $\lambda_{tot} = 2.17$.