Absorption and photoemission spectroscopy of rare-earth oxypnictides

The electronic structure of various rare-earth oxypnictides has been investigated by performing Fe L-2,L-3 x-ray absorption spectroscopy, and Fe 2p and valence band x-ray photoemission spectroscopy. As representative samples the non-superconducting parent compounds LnFeAsO (Ln = La, Ce, Sm and Gd) have been chosen and measured at 25 and 300 K, i.e. below and above the structural and magnetic phase transition at similar to 150 K. We find no significant change of the electronic structure of the FeAs layers when switching between the different rare-earth ions or when varying the temperature below and above the transition temperatures. Using a simple two-configuration model, we find qualitative agreement with the Fe 2p(3/2) core-level spectrum, which allows for a qualitative explanation of the experimental spectral shapes.