Transition to nonmagneticfstates in Ce intermetallic compounds studied by bremsstrahlung isochromat spectroscopy

Abstract

Bremsstrahlung isochromat spectra (BIS) of La and Ce intermetallic compounds with Co, Ni, Pd, Ru, Pt, and Au are presented. Final states with one and two $f$ electrons are detected in trivalent La and Ce compounds, respectively. In contrast, in nonmagnetic Ce compounds, such as many of those with transition metals, transitions to final states with both one and two $f$ electrons are observed. From the positions of the Ce BIS peaks it can be inferred that the effective Coulomb correlation energy of the Ce $f$ electrons is not strongly dependent on chemical environment, and in all cases studied it is much larger than the hybridization width. The weights of the BIS $f^1$ and $f^2$ final states are not the same as those found in x-ray absorption (XAS) or x-ray photoemission (XPS) spectroscopies. From this it must be concluded that the $f$ states are appreciably hybridized with the conduction states, and the necessity of a dynamic many-body description of the spectroscopic data (and consequently also of the Ce ground state) emerges clearly once more. We show that the discrepancy between XPS, XAS, and BIS intensity can be greatly reduced by calculations based on an extended Anderson model using the same set of parameters for all techniques and imply that this model must contain much of the relevant physics. The comparison of theory and experiment leads us to infer a hybridization $\Delta$ of the $f$ levels which exceeds those accepted thus far by a factor of 5-10.