Superfluid density of Ba(Fe1-xMx)2As2 from optical experiments

The temperature dependence of the ab-plane optical reflectivity of Ba(Fe0.92Co0.08)(2)As-2 and Ba(Fe-0.95 Ni-0.05)(2)As-2 single crystals is measured in a wide spectral range. Upon entering the superconducting regime, the reflectivity in both compounds increases considerably at low-frequency, leading to a clear gap in the optical conductivity below 100 cm(-1). From the analysis of the complex conductivity spectra we obtain the penetration depth lambda(T) = (3500 +/- 350) angstrom for Ba(Fe0.92Co0.08)(2)As-2 and (3000 +/- 300) angstrom for Ba(Fe0.95Ni0.05)(2)As-2. The calculated superfluid density rho(s) of both compounds nicely fits Homes' scaling relation rho(s) = (125 +/- 25)sigma T-dc(c) . (C) 2009 Elsevier B.V. All rights reserved.