High-energy spectroscopy in uranium-based systems

We have carried out high-energy spectroscopy measurements (x-ray photoemission on the 4f core level, ultraviolet spectroscopy on the valence band, and bremsstrahlung isochromat spectroscopy) on UPd₃, UPt₃, and URh₃ compounds. A progressive localization of the 5f states is expected throughout this series: the 5f electrons are usually considered to be itinerant in URh₃, localized in UPd₃, and UPt₃ is a heavy-fermion compound. We show that the different spectroscopic measurements cannot be explained with one-electron band-structure calculations and are best analyzed in terms of the Anderson-impurity model. Many-body effects dominate the spectral functions, suggesting that the correlations between the 5f electrons play an essential role in the uranium compounds.