Appearance of correlation effects in U intermetallics

Experimental densities of states of USi/sub 3/ and UIr/sub 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 USi/sub 3/, whereas the unoccupied states of UIr/sub 3/ exhibit a satellite which cannot be explained by the one-particle calculation. The satellite in BIS of UIr/sub 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.