Appearance of Correlation Effects in U Intermetallics

Experimental densities of states of U${\mathrm{Si}}_3$ and U${\mathrm{Ir}}_3$ 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 U${\mathrm{Si}}_3$, whereas the unoccupied states of U${\mathrm{Ir}}_3$ exhibit a satellite which cannot be explained by the one-particle calculation. The satellite in BIS of U${\mathrm{Ir}}_3$ 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.