X-ray absorption spectra in rare-earth and uranium intermetallics: Localized versus itinerant final states

We report $L_{\mathrm{I}}$ and $L_{\mathrm{III}}$ x-ray absorption spectra for a series of rare-earth (RE) intermetallics and $L_{\mathrm{III}}$ and $M_{\mathrm{V}}$ spectra for uranium intermetallics. Many of the features can be understood in terms of one-electron band theory; for example, the tendency of the absorption maxima to grow stronger and narrower in the sequence U $L_{\mathrm{III}}$, RE $L_{\mathrm{III}}$, and U $M_{\mathrm{V}}$ reflects the increasing density of states in the sequence U $6d$, RE $5d$, and U $5f$. Deviations from band theory are apparent in the systematics of the transition energies: For example, all the Ce $L_{\mathrm{III}}$ transitions occur at the same energy as do the U $M_{\mathrm{V}}$ transitions, but the U $L_{\mathrm{III}}$ and Ce $L_{\mathrm{I}}$ show substantial chemical shifts as expected in one-electron theory. The data taken together suggest that the core hole tends to localize the final $4f$ and $5d$ transition states in the rare-earth elements and the $5f$ in the actinides but not the $6d$ in the actinides nor the $\mathrm{sp}$ states in either case. The discussion is cast in terms of recent theories of the effect of the core-hole potential.