X-ray spectra and electronic structure of FeAs superconductors release_a4jqb6uad5awnfgklmrfiaepje

Abstract

The densities of the valence and conduction band electronic states of the newly discovered layered superconductors LaOFeAs, LaO_0.87F_0.13FeAs (Tc=26 K), SmO_0.95F_0.05FeAs and SmO_0.85F_0.15FeAs (Tc=43 K) are studied using soft X-ray absorption and emission spectroscopy combined with FP LAPW calculations of LaOFeAs, LaO_0.875FeAs and LaO_0.875F0.125FeAs. The Fe 3d-states are localized in energy near the top of the valence band and are partially hybridized with p-type O (2p), As (4p), and La (6p) states approximately 3 eV below the Fermi energy. The Fe L3 X-ray emission spectra do not show any features that would indicate the presence of the low Hubbard 3d-band or the quasiparticle peak that were predicted by the DMFT analysis of LaOFeAs. We can conclude that the LaOFeAs-type compounds do not represent strongly correlated systems. When either oxygen vacancies or fluorine dopants are included in numerical electronic structure calculations the width of O 2p-band decreases, but the distribution of Fe 3d-states is largely unaffected.
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