Applicability of the Single Impurity Model to Photoemission Spectroscopy of Heavy Fermion Ce Compounds

Photoemission spectra measured with an energy resolution of 5 meV from Ce-based heavy fermion materials are presented. The spectra add strong support to the interpretation of the peak at the Fermi level in terms of the spectral function calculated within the single impurity model. This work clearly demonstrates that if reliable information on heavy fermion compounds is to be obtained using photoemission spectroscopy, it is necessary to work with an instrumental resolution approaching ${\mathrm{kT}}_K$, where $T_K$ is the Kondo temperature.