Stabilizing the U 5f ² configuration in the U³⁺ compound UTe₂: importance of U 6d

We have investigated UTe₂, proposed to be a topological spin-triplet superconductor, with high-resolution valence band resonant inelastic x-ray scattering at the U M_4,5-edges. We observe atomic-like low energy excitations which establish the correlated nature of the material. These excitations originate from the U 5f ² configuration, which is surprising in view of the expected formal U³⁺ valence based on the presence of short Te2-Te2 distances in the crystal. Supported by band structure calculations, we infer that the stabilization of the U 5f ² configuration is the result of the U 6d states acting as a reservoir to absorb the extra charge from the Te2 sublattice. We suggest that the formal configuration of uranium in UTe₂ should be written as 5f²6d¹, thereby indicating that the description of the physical properties should start from a 5f ² Ansatz.