probed by directional dependence of nonresonant inelastic x-ray scattering*

Core-level nonresonant inelastic x-ray scattering (NIXS) [1-3], also called x-ray Raman scattering, has been performed on single crystals of UO₂ to study the directional dependence of higher-order multipole scattering from the uranium O_4,5 edges (90–110 eV). By comparing the experimental results with theoretical calculations the symmetry of the ground state is confirmed directly as the crystal-field Γ₅ triplet state within the J = 4 manifold [4] as had been suggested by inelastic neutron scattering [5]. The results demonstrate that the directional dichroism of the NIXS spectra is sensitive to the CF strength and establish NIXS as a tool for probing crystal-field interactions quantitatively.

[1] M.W. Haverkort et al., Phys. Rev. Lett. 99 257401 (2007)
[2] R. Caciuffo et al., Phys. Rev. B 81 195104 (2010)
[3] M. Sundermann et al., PNAS 113 13989 (2016)
[4] M. Sundermann et al., Phys. Rev. B 98 205108 (2018)
[5] G. Amoretti et al., Phys. Rev. B 40 1856 (1989)