Angular dependence of x-ray absorption spectrum for field-aligned iron-based superconductors

Anisotropic FeK -edge and AsK -edge x-ray absorption near-edge spectrum measurements on superconducting (Tc =52 K) (Sm0.95 La0.05) FeAs (O0.85 F0.15) field-aligned microcrystalline powder are presented. The angular dependence of Fe pre-edge peak (dipole transition of Fe1s electrons to Fe3d/As4p hybrid bands) relative to the tetragonal ab plane of aligned powder indicates larger density of state along the c axis and is consistent with the local-density approximation band-structure calculation. The anisotropic FeK -edge spectra exhibit a chemical shift to lower energy compared to FeO which are closely related to the itinerant character of Fe2+ 3 d6 orbitals. The anisotropic AsK -edge spectra are more or less the mirror images of FeK edge due to the symmetrical Fe-As hybridization in the FeAs layer. Angular dependence of As main peak (dipole transition of As1s electrons to higher-energy hybrid bands) was observed suggesting character of As4d eg orbitals.