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

Abstract

Anisotropic $\text{Fe}\text{ }K$-edge and $\text{As}\text{ }K$-edge x-ray absorption near-edge spectrum measurements on superconducting $({T}_{c}=52\text{ }\text{K})$ $({\text{Sm}}_{0.95}{\text{La}}_{0.05})\text{FeAs}({\text{O}}_{0.85}{\text{F}}_{0.15})$ field-aligned microcrystalline powder are presented. The angular dependence of Fe pre-edge peak (dipole transition of $\text{Fe}\text{ }1s$ electrons to $\text{Fe}\text{ }3d/\text{As}\text{ }4p$ 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 $\text{Fe}\text{ }K$-edge spectra exhibit a chemical shift to lower energy compared to FeO which are closely related to the itinerant character of ${\text{Fe}}^{2+}\text{ }3{d}^{6}$ orbitals. The anisotropic $\text{As}\text{ }K$-edge spectra are more or less the mirror images of $\text{Fe}\text{ }K$ edge due to the symmetrical Fe-As hybridization in the FeAs layer. Angular dependence of As main peak (dipole transition of $\text{As}\text{ }1s$ electrons to higher-energy hybrid bands) was observed suggesting character of $\text{As}\text{ }4d\phantom{\rule{0.4em}{0ex}}{e}_{g}$ orbitals.