Resonant inverse photoemission in cerium-based materials

The Ce 4f part of the electron addition spectra of cerium compounds is selectively and resonantly enhanced when the excitation energy coincides with the Ce 3d→4f (${\mathrm{M}}_{4,5}$) absorption edge. Different spectral features, corresponding to ${4\mathrm{f}}^1$ and ${4\mathrm{f}}^2$ configurations in the final state, exhibit distinct resonance profiles. The relative intensities of the ${\mathrm{f}}^1$ and ${\mathrm{f}}^2$ resonances may vary by as much as a factor of 50, according to the strength of the hybridization between 4f and conduction-band states. At resonance the spectral line shape is unambiguously modified when the temperature is varied across the characteristic Kondo temperature.