Spectroscopic evidence for the 5f Coulomb interaction in UAl2 and UPt3

Interpretation of resonant photoemission spectra of solid actinide systems

It is shown that valence-band photoemission (PE) spectra of epitaxial hcp films of U metal may be understood within a one-step model of PE based on an itinerant description of the U 5f states. Particularly, the PE intensities of the f-derived bands are correctly reproduced for photon energies between 60 and 103 eV. It is found that a cross-section minimum of the Fermi-energy feature at h(nu) = 90-94 eV, which previously was assigned to a Fano antiresonance at the 5d-->5f excitation threshold, is mainly caused by a Cooper minimum. Analogous 5f cross-section variations in the region of the 5d-->5f resonances were obtained for UPd3 and Pu metal.

Cooper minima in the photoemission spectra of solids

Variations of the photoionization cross section of valence states as a function of interatomic distance are studied by means of atomic and solid-state density functional approaches and compared with photoemission data. In contrast to the free atom case, a series of Cooper minima is found for 4d, 5d, and 5f states in Pd, Ag, Au, and U metals. The discovered fundamental phenomenon is of high importance for the correct interpretation of photoemission data.