Eur. Phys. J. B 77, 25-30 (2010)
https://doi.org/10.1140/epjb/e2010-00242-y

Multi-gap superconductivity in a BaFe_1.84Co_0.16As₂ film from optical measurements at terahertz frequencies

¹ Sincrotrone Trieste S.C.p.A., S.S. 14 km 163.5, in Area Science Park, 34012 Basovizza (Trieste), Italy
² CNR-IOM and Dipartimento di Fisica, Universitá di Roma Sapienza, P.le A. Moro 2, 00185 Rome, Italy
³ Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, FL, 32310, USA
⁴ Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
⁵ CNR-SPIN and Dipartimento di Fisica, Universitá di Genova, Via Dodecaneso 33, 16146 Genova, Italy
⁶ CNR-SPIN and Dipartimento di Fisica, Universitá di Roma “La Sapienza", P.le A. Moro 2, 00185 Rome, Italy

Corresponding author: ^a andrea.perucchi@elettra.trieste.it

Received: 1 March 2010
Revised: 8 June 2010
Published online: 6 August 2010

Abstract

We measured the THz reflectance properties of a high quality epitaxial thin film of the Fe-based superconductor BaFe_1.84Co_0.16As₂ with T_c = 22.5 K. The film was grown by pulsed laser deposition on a DyScO₃ substrate with an epitaxial SrTiO₃ intermediate layer. The measured R_S/R_N spectrum, i.e. the reflectivity ratio between the superconducting and normal state reflectance, suggests the presence of a superconducting gap Δ_A close to 15 cm^-1. A detailed data analysis shows that a two-band, two-gap model is necessary to obtain a good description of the measured R_S/R_N spectrum. The low-energy Δ_A gap results to be well determined (Δ_A = 15.5±0.5 cm^-1), while the value of the high-energy gap Δ_B is more uncertain (Δ_B = 55±7 cm^-1). Our results provide evidence of two electronic contributions to the system conductivity with the presence of two optical gaps corresponding to 2Δ/kT_c values close to 2 and 7.