Insight into the physics of Fe-pnictides from optical and T=0 penetration depth data

We report theoretical Drude plasma frequencies (PF) Omega(p) for 12 Fe-pnictides from density functional theory (DFT) based calculations and compare them with experimental PF from reflectivity data. The observed renormalization points to moderate many-body effects beyond the DFT like in ordinary transition metals. From large empirical background dielectric constants epsilon(infinity) = 12 - 13, we estimate a large As or P polarizability which significantly reduces the Hubbard U-d approximate to 4 eV as suggested by bad metal scenarios to below 2 eV pointing to rather strong polaronic effects as suggested by G. Sawatzky et al. Europhys. Lett. 86 (2009) 17006. From the mu SR penetration depth at T = 0 and the Omega(p) from optics, we estimate the total el-boson coupling constant lambda(tot) approximate to 0.6 +/- 0.25 for LaFeAsO0.9F0.1 using Eliashberg-theory and arrive at the quasi-clean limit. (C) 2009 Elsevier B.V. All rights reserved.