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

Anisotropic Fe K-edge and As K-edge x-ray absorption near-edge spectrum measurements on superconducting (T-c=52 K) (Sm0.95La0.05)FeAs(O0.85F0.15) field-aligned microcrystalline powder are presented. The angular dependence of Fe pre-edge peak (dipole transition of Fe 1s electrons to Fe 3d/As 4p 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 Fe K-edge spectra exhibit a chemical shift to lower energy compared to FeO which are closely related to the itinerant character of Fe2+ 3d(6) orbitals. The anisotropic As K-edge spectra are more or less the mirror images of Fe K edge due to the symmetrical Fe-As hybridization in the FeAs layer. Angular dependence of As main peak (dipole transition of As 1s electrons to higher-energy hybrid bands) was observed suggesting character of As 4d e(g) orbitals.