Transmittance and reflectance measurements at terahertz frequencies on a superconducting BaFe_{1.84}Co_{0.16}As_2 ultrathin film: an analysis of the optical gaps in the Co-doped BaFe_2As_2 pnictide

Abstract

Here we report an optical investigation in the terahertz region of a 40 nm ultrathin BaFe${}_{1.84}$Co${}_{0.16}$As${}_2$ superconducting film with superconducting transition temperature T${}_c$ = 17.5 K. A detailed analysis of the combined reflectance and transmittance measurements showed that the optical properties of the superconducting system can be described in terms of a two-band, two-gap model. The zero temperature value of the large gap ${\Delta }_B$, which seems to follow a BCS-like behavior, results to be ${\Delta }_B$(0) = 17 cm${}^{-1}$. For the small gap, for which ${\Delta }_A$(0) = 8 cm${}^{-1}$, the temperature dependence cannot be clearly established. These gap values and those reported in the literature for the BaFe${}_{2-x}$Co${}_x$As${}_2$ system by using infrared spectroscopy, when put together as a function of T${}_c$, show a tendency to cluster along two main curves, providing a unified perspective of the measured optical gaps. Below a temperature around 20 K, the gap-sizes as a function of T${}_c$ seem to have a BCS-like linear behavior, but with different slopes. Above this temperature, both gaps show different supra-linear behaviors.

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Cited by in corpus (4)

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• Electrodynamics of superconducting pnictide superlattices
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