U 5$f$ crystal-field ground state of UO$_2$ probed by directional dichroism in nonresonant inelastic x-ray scattering

TL;DR

This study uses directional dichroism in nonresonant inelastic x-ray scattering to directly confirm the crystal-field ground state of UO$_2$ as a $$ triplet within the $J=4$ manifold, demonstrating NIXS's potential for probing crystal-field interactions.

Contribution

The paper provides the first direct confirmation of the UO$_2$ ground state symmetry using NIXS and shows its sensitivity to crystal-field strength, advancing the technique's application.

Findings

Confirmed UO$_2$ ground state as $$ triplet within $J=4$ manifold.

Demonstrated NIXS's sensitivity to crystal-field strength.

Established NIXS as a quantitative tool for crystal-field interactions.

Abstract

Nonresonant inelastic x-ray scattering (NIXS) has been performed on single crystals of UO$_2$ to study the direction 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 (CF) $\Gamma_5$ triplet state within the $J$ = 4 manifold. The results also demonstrate that the directional dichroism of the NIXS spectra is sensitive to the CF strength and establish NIXS as a tool for probing CF interactions quantitatively.