Electron-spectroscopic manifestations of the4fstates in light rare-earth solids

The consequences of the degeneracy between configurations with different populations of atomiclike f states are studied systematically for a number of light rare-earth materials (Ba, ${\mathrm{LaF}}_3$, ${\mathrm{La}}_2$ ${\mathrm{O}}_3$, La, ${\mathrm{CeO}}_2$, ${\mathrm{CeCo}}_2$, CeN, α-Ce, and γ-Ce) using high-energy spectroscopies. The Anderson impurity model applied to this problem (Gunnarsson-Schönhammer model) is found to describe convincingly a variety of electron-spectroscopic excitations, such as, x-ray photoemission and bremsstrahlung isochromat spectroscopy. We have extended this many-body formalism to account for electron-energy loss spectroscopy and $L_{\mathrm{III}}$ absorption edges. The parameters resulting from the calculation are analyzed within the framework of a simplified Hamiltonian containing no coupling terms between f and band states. This approach reveals in a natural way the importance of the conventional concept of hybridization. The energy degeneracy and the wave-function overlap of quantum states give rise to a mixing and to a continuous energy distribution of excitations. For electronic transitions described within the sudden approximation the impurity model provides a sound and unified description of the ‘‘satellite complex’’ encountered in the high-energy excitation spectra of such systems.