Electronic structure of LaFeAsO1-xFx from x-ray absorption spectroscopy

We investigated the recently found superconductor LaFeAsO1-xFx by x-ray absorption spectroscopy. From a comparison of the O K edge with LDA calculations we find good agreement and are able to explain the structure and changes in the spectra with electron doping. From experimental Fe L-2,L-3-edge spectra and charge-transfer multiplet calculations we gain further information on important physical values such as the hopping parameters, the charge-transfer energy Delta, and the Hubbard U. Furthermore we find the system to be very covalent with a large amount of ligand holes. A shift in the chemical potential is visible in the O K- and Fe L-2,L-3-edge spectra which emphasizes the importance of band effects in these compounds. From the entirety of our results we conclude that LaFeAsO is a bandwidth-dominated material.