A series of cerium heavy fermion compounds have been studied in order to check for the systematics with TK and the temperature dependence of the Kondo resonance predicted by the Kondo model. Neither the systematics nor the temperature dependence is found, the latter primarily determined from a detailed study in CeSi2. The qualitative shapes of the features at EF remain nearly constant irrespective of TK, while all the temperature dependence can be explained as resulting from phonon broadening of core-like states as well as Fermi function broadening. In addition, if the d electron contribution to the spectra is subtracted, one obtains a symmetric, lorentzian line shape for the "main" 4f peak. © 1992.

4f levels in Ce heavy-fermion compounds are examined using resonant photoemission. We find the following inconsistencies with the predictions of the Kondo model: (a) All temperature dependence can be accounted for simply by phonon broadening and the Fermi function; (b) the spectral weights of the features near EF do not scale with TK; and (c) the line shape of the feature previously identified as the Kondo resonance is Lorentzian and about an order of magnitude broader than predictions. Instrument resolution is not a limiting factor. © 1992 The American Physical Society.

We report valence band photoemission results for YbCu2Si2, The 4f13(J = 7 2) final state peak, centered 60 meV below the Fermi level ε{lunate}F, lacks the temperature dependence and is broader than predicted for a Kondo resonance. Together with recent photoemission results for cerium compounds, these results raise serious doubts about the Kondo impurity explanation of heavy fermion photoemission. © 1992.

The electronic properties of single crystal YbInCu4 and YbAgCu4 have been investigated by means of high resolution photoelectron spectroscopy. A first order, isostructural phase transition for YbInCu4 at 42 K leads to changes in the Kondo temperature, of more than an order of magnitude. This phase transition and accompanying Kondo temperature change provide the most direct test of the single impurity model to date. The photoemission results are incongruous with the single impurity model predictions for temperature dependence, binding energy and 4f occupancy, encouraging a re-evaluation of the single impurity model applicability. © 1999 Taylor & Francis Group, LLC.

We present valence-band photoemission spectra for CeAl3, CeBe13, CeSi2, CeCu2Si2, and related conventional rare-earth counterpart compounds, taken at photon energies corresponding to the giant 4d resonance with resolution ∼150 meV. We take into account the 5d emission, which comprises 30% of the valence-band emission at the 4d resonance. We compare the resulting 4f emission to the predictions of the Anderson impurity model calculated in a low-order 1/N expansion, and including spin-orbit, crystal-field, and finite Coulomb correlation effects. The calculation gives order-of-magnitude fits to the data, but underestimates the spectral weight near the Fermi level by a factor of 2 and overestimates the width of the main f emission at 2 eV by a factor of 4. We argue that Ce photoemission remains an open problem and discuss several experimental and theoretical issues which need to be resolved to make further progress. © 1993 The American Physical Society.

The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow, nearly temperature-independent bands (i.e., no spectral weight loss or transfer with temperature). A small dispersion of the f-bands above the Kondo temperature is easily measurable so that a Kondo resonance, as defined by NCA, is not evident. Preliminary results, however, indicate that the Periodic Anderson Model (PAM) captures some of the essential physics. Angle-integrated resonant photoemission results on δ-Pu indicate a narrow 5f feature at EF, similar in width to f-states in Ce and U compounds, but differing in that PES cross-section as a function of hv suggests substantial 6d admixture. © 1998 Elsevier Science S.A.

We report high-resolution photoemission results for the 4f levels in YbCu2Si2 and CeSi2. The data are compared to the predictions of the Anderson impurity model for valence band photoemission. These predicted spectra are obtained both in an approximate fashion by broadening crystal field (CF) states whose parameters are determined from existing neutron scattering data, as well as from a Gunnarson-Schonhammer calculation. Inclusion of crystal fields does not affect our two fundamental conclusions: that there is a natural linewidth in the problem (≈130meV) which is much greater than predicted by the Anderson model, and that the expected temperature dependence of the Kondo resonance is absent. Due to the large natural linewidth, experimental resolution (60-95meV) is not a limiting factor. © 1992.

We report evidence of 4f band character in Ce 4f states at T ≫ TK using high-resolution angle-resolved resonant photoemission. The Ce intermetallic compound CePt2+x was grown and studied in situ by the method of MBE and was characterized by LEED, XPS and XAS. These new findings suggest a need for a re-examination of 4f photoemission in Ce compounds. © 1995.