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

Abstract

We report theoretical Drude plasma frequencies (PF) Ωp 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 ε∞=12-13, we estimate a large As or P polarizability which significantly reduces the Hubbard Ud≈4eV as suggested by bad metal scenarios to below 2eV pointing to rather strong polaronic effects as suggested by G. Sawatzky et al. Europhys. Lett. 86 (2009) 17006. From the μSR penetration depth at T=0 and the Ωp from optics, we estimate the total el–boson coupling constant λtot≈0.6±0.25 for LaFeAsO0.9F0.1 using Eliashberg-theory and arrive at the quasi-clean limit.