paper

Multi-gap superconductivity in a BaFe1.84Co0.16As2 film from optical measurements at terahertz frequencies

arXiv:1003.0565 · doi:10.1140/epjb/e2010-00242-y

Abstract

We measured the THz reflectance properties of a high quality epitaxial thin film of the Fe-based superconductor BaFe $_{1.84}$ Co $_{0.16}$ As $_{2}$ with T $_{c}$ =22.5 K. The film was grown by pulsed laser deposition on a DyScO $_{3}$ substrate with an epitaxial SrTiO $_{3}$ intermediate layer. The measured $R_{S} / R_{N}$ spectrum, i.e. the reflectivity ratio between the superconducting and normal state reflectance, provides clear evidence of a superconducting gap $I^_{A}$ close to 15 cm $^{- 1}$ . A detailed data analysis shows that a two-band, two-gap model is absolutely necessary to obtain a good description of the measured $R_{S} / R_{N}$ spectrum. The low-energy $I^_{A}$ gap results to be well determined ( $I^_{A}$ =15.5 $\pm$ 0.5 cm $^{- 1}$ ), while the value of the high-energy gap $I^_{B}$ is more uncertain ( $I^_{B}$ =55 $\pm$ 7 cm $^{- 1}$ ). Our results provide evidence of a nodeless isotropic double-gap scenario, with the presence of two optical gaps corresponding to 2 $I^/ k T_{c}$ values close to 2 and 7.

Published Version