Hybridization effects in unoccupied 4f states of Ce compounds

An energy shift of the f(2) feature is detected between inverse photoemission surface and bulk f Line shapes in Ce compounds. A comparison with analogous Lu compounds shows a systematic enhancement of the 4f surface shift in the case of Ce (up to 0.3 eV). This effect is interpreted as an extra ''hybridization shift'' in good agreement with the results of an Anderson impurity Hamiltonian calculation. These findings show that the on-site f-f correlation energy does not increase at the surface indicating unchanged screening dynamics despite the reduced nearest-neighbors coordination.