Common Features in Electronic Structure of the Oxypnictide Superconductors from Photoemission Spectroscopy

High resolution photoemission measurements are carried out on non-superconducting LaFeAsO parent compound and various superconducting RFeAs(O1-xFx) (R=La, Ce and Pr) compounds. It is found that the parent LaFeAsO compound shows a metallic character. By extensive measurements, several common features are identified in the electronic structure of these Fe-based compounds: (1) 0.2 eV feature in the valence band, (2) a universal 13-16 meV feature, (3) near Ef spectral weight suppression with decreasing temperature. These universal features can provide important information about band structure, superconducting gap and pseudogap in these Fe-based materials.