Identifying f-electron valence and correlations in UTe₂ with O-edge resonant inelastic X-ray scattering

The recent discovery of spin-triplet superconductivity emerging from a non-magnetic parent state in UTe₂ has stimulated great interest in the underlying mechanism of Cooper pairing. For the electron configuration of uranium in UTe₂, there is an active debate between 5f²6d¹-based models with singlet crystal field states versus 5f³-based models that predict atomic Kramers doublets and much greater 5f itinerancy. I will present resonant inelastic X-ray scattering (RIXS) and X-ray absorption spectroscopy (XAS) measurements, comparing with our atomic multiplet-based modeling. The XAS and RIXS data are found to agree strongly with predictions for a 5f²6d¹-like valence electron configuration with weak intra-dimer magnetic correlations, and provide a new context for interpreting recent investigations of the electronic structure and superconducting pairing mechanism.