Measurement of f orbital hybridization in rare earths through electric dipole-octupole interference in x-ray absorption spectroscopy

This work provides a direct route to measure the degree of hybridization of f states in rare earths. The
interference between electric dipole and octupole transitions is measured at the L1 edge of Gd in Gd3Ga5O12
using x-ray natural linear dichroism (XNLD) and high energy resolution fluorescence detection. The Gd 4 f -6p
admixture is quantified through the integral of the dipole-octupole XNLD using a sum rule easily applicable to
experimental data. The mixing of the Gd valence states with the O ligand orbitals, calculated from first principles,
reveals that despite their localized character, the Gd 4 f orbitals mix with the O 2p and 2s orbitals with an
antibonding and bonding character, respectively.