Optical properties of BaFe_2-xCo_xAs₂

We present detailed temperature-dependent optical data on BaFe2-xCoxAs2 (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 at energies as low as 10 meV. We determine the superfluid density rho(s)/(2 pi c)(2) = 2.2 +/- 0.5.10(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 +/- 0.8 meV. In addition, from comparing the experimental spectra to model calculations we obtain indications for an additional band of strongly scattered carriers with a larger gap, 2 Delta(2) = 14 +/- 2 meV. Copyright (C) EPLA, 2010