Polarized x-ray absorption spectra of CuGeO₃ at the Cu and Ge K edges

Polarized x-ray absorption near edge structure (XANES) spectra at both the Cu and Ge K edges of CuGeO₃ are measured and calculated relying on the real-space multiple-scattering formalism within a one-electron approach. The polarization components are resolved not only in the unit cell coordinate system (ɛ‖a, ɛ‖b, ɛ‖c) but also in a local frame attached to the nearest neighborhood of the photoabsorbing Cu atom. In that way, features which resist a particular theoretical description can be identified. We have found that it is the out-of-CuO₄-plane p_z^′ component which defies the one-electron calculation based on the muffin-tin potential. For the Ge K edge XANES, the agreement between the theory and the experiment appears to be better for those polarization components which probe more compact local surroundings than for those which probe regions with lower atomic density.