Two-band Bardeen-Cooper-Schrieffer superconducting state of the iron pnictide compound Ba(Fe0.9Co0.1)2As2

The optical conductivity and permittivity spectra of Ba(Fe0.9Co0.1)(2)As-2 films (T-c = 20 K) are analyzed together with the literature data on photoemission and specific heat. In the superconducting state at all temperatures up to T-c the temperature dependence of the magnetic field penetration depth is well described within the generalized two-band BCS model with intraband and interband pairing interactions considered. It is shown that the small superconducting energy gap 2 Delta((1)) = 3.7 meV develops in the electron subsystem while the larger gap 2 Delta((2)) = 7.9 meV opens in the hole subsystem. The normal state parameters, such as plasma frequency and scattering rate, of electron and hole conduction bands are determined.