Appearance of Correlation Effects in U Intermetallics

Experimental densities of states of USi₃ and UIr₃ obtained by x-ray photoelectron spectroscopy and bremsstrahlung isochromat spectroscopy (BIS) are compared to fully relativistic self-consistent band-structure calculations. Very good agreement is found for USi₃, whereas the unoccupied states of UIr₃ exhibit a satellite which cannot be explained by the one-particle calculation. The satellite in BIS of UIr₃ is attributed to a quasiparticle bound state, and is qualitatively reproduced by a Hubbard model including Coulomb correlation within the narrow $5f$ band. The importance of our findings with reference to the magnetic properties of U intermetallics as well as pure U metal is discussed.