Electronic properties of4fsubstances at configuration crossover

Abstract

In a system of concentrated $4f$ ions with two configurations $4{f}^{n}$ and $4{f}^{n\ensuremath{-}1}$ competing for stability, a narrow resonance in the electronic density of states near the Fermi energy is expected. Using an explicitly configuration-based approach with appropriate intraconfigurational splittings included, we obtain a sum rule on the integrated density of states and a microscopic estimate of the resonance width. The width, identifiable with an interconfiguration fluctuation rate, is proportional to the nominal mixing width $\ensuremath{\Delta}({\ensuremath{\epsilon}}_{F})=\ensuremath{\pi}{|{V}_{\mathrm{mix}}|}^{2}{\ensuremath{\rho}}_{\mathrm{cond}}({\ensuremath{\epsilon}}_{F})$, but with a proportionality factor depending rather strongly upon the specific ionic states involved. Results are obtained for electronic specific heats, x-ray photoemission linewidths, and M\"ossbauer spectra in such systems.