Evidence for weak electronic correlations in iron pnictides

Abstract

Using x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS), charge dynamics at and near the $\text{Fe}\text{ }L$ edges is investigated in Fe-pnictide materials and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show that Coulomb correlations are much smaller than in the cuprates, highlighting the role of Fe metallicity and strong covalency in these materials. The best agreement with experiment is obtained using Hubbard parameters $U\ensuremath{\lesssim}2\text{ }\text{eV}$ and $J\ensuremath{\approx}0.8\text{ }\text{eV}$.