Optical properties of BaFe$_{2-x}$Co$_x$As$_2$

TL;DR

This study provides detailed temperature-dependent optical data on BaFe$_{2-x}$Co$_x$As$_2$, revealing insights into its interband conductivity, superfluid density, and multiple superconducting gaps.

Contribution

It offers the first detailed optical analysis of BaFe$_{2-x}$Co$_x$As$_2$ across a broad energy range, identifying multiple superconducting gaps and their implications.

Findings

Interband conductivity starts around 10 meV.

Superfluid density is 2.2 x 10^{7} cm^{-2}.

Presence of two superconducting gaps, 6.2 meV and 14 meV.

Abstract

We present detailed temperature dependent optical data on BaFe$_{2-x}$Co$_{x}$As$_{2}$ (BCFA), with x = 0.14, between 4 meV and 6.5 eV. We analyze our spectra to determine the main optical parameters and show that in this material the interband conductivity already starts around 10 meV. We determine the superfluid density to be 2.2 10^{7}$ cm^{-2}, which places optimally doped BFCA close to the Uemura line. Our experimental data shows clear signs of a superconducting gap with 2$\Delta_{1}$ = 6.2 $\pm$ 0.8 meV. In addition we show that the optical spectra are consistent with the presence of an additional band of strongly scattered carriers with a larger gap, 2$\Delta_{2}$ = 14 $\pm$ 2 meV.