Identifying valence structure in LiFeAs and NaFeAs with core-level spectroscopy.

Resonant x-ray emission spectroscopy (XES) measurements at Fe L(2,3) edges and electronic structure calculations for LiFeAs and NaFeAs are presented. Experiment and theory show that in the vicinity of the Fermi energy, the density of states is dominated by contributions from Fe 3d states. The comparison of Fe L(2,3) XES with spectra of related FeAs compounds reveals similar trends in energy and the ratio of intensities of the L(2) and L(3) peaks (I(L(2))/I(L(3)) ratio). The I(L(2))/I(L(3)) ratio for all FeAs-based superconductors is found to be closer to that of metallic Fe than that of the strongly correlated FeO. We conclude that iron-based superconductors are weakly or, at most, moderately correlated systems.