Optical response of FeAs-based compounds

We investigated the optical properties of FeAs-based compounds. The optical conductivity spectrum of undoped CaFe2As2 shows an abrupt opening of a gap below the magnetic/structural transition temperature (T-N). The low-energy spectrum above T-N is composed of two components: one is a coherent Drude term and the other is an incoherent one. Below T-N, the Drude term becomes very narrow without changing its weight, and a gap seems to open in the incoherent term. The two-component feature also exists in the spectrum of superconducting Ba(Fe0.92Co0.08)(2)As-2 and a superconducting gap opens in both components. The London penetration depth calculated from the spectral weight analysis is similar or equal to 2770 angstrom consistent with other experiments. (C) 2009 Published by Elsevier B.V.