X-ray spectra and electronic structure of FeAs superconductors

TL;DR

This study investigates the electronic structure of FeAs-based superconductors using X-ray spectroscopy and calculations, revealing localized Fe 3d-states and challenging the notion of strong electron correlations in these materials.

Contribution

It provides new insights into the electronic states of FeAs superconductors, showing the absence of predicted Hubbard bands and clarifying the role of doping and hybridization.

Findings

Fe 3d-states are localized near the valence band top

No evidence of low Hubbard 3d-band in spectra

FeAs compounds are not strongly correlated systems

Abstract

The densities of the valence and conduction band electronic states of the newly discovered layered superconductors LaOFeAs, LaO$_{0.87}$F$_{0.13}$FeAs (Tc=26 K), SmO$_{0.95}$F$_{0.05}$FeAs and SmO$_{0.85}$F$_{0.15}$FeAs (Tc=43 K) are studied using soft X-ray absorption and emission spectroscopy combined with FP LAPW calculations of LaOFeAs, LaO$_{0.875}$FeAs and LaO$_{0.875}$F${0.125}$FeAs. 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.