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.

We have measured the temperature dependence between 80 and 300 K and spectral weight of the 4f features in clean single crystal Yb heavy fermions, cleaved in a vacuum of 5 × 10-11 Torr. A small (∼ 15%) decrease in spectral weight differs substantially from the reported ∼ 50% decrease over this range. All divalent features are much larger than expected, yielding nf values far too small. The intensity of the divalent features in YbAuCu4 is about two orders of magnitude larger than expected. © 1994.

A high-resolution photoemission (PES) study of the heavy-fermion compound YbAl3 has been undertaken to test the qualitative and quantitative predictions of the single-impurity model. Corroborating data on YbAgCu4 and YbCu2Si2 are also presented. For Yb-based heavy fermions the model predicts a fully occupied Kondo resonance so that its width, intensity, and temperature dependence should be directly accessible by PES. Due to the existence of temperature- and/or contamination-dependent surface features, which are not dealt with by the model, a rigorous normalization and curve-fitting procedure was required to extract the bulk 4f line shape. For the particular temperature cycling method employed by us, we do not observe any temperature dependence in the peak that had been previously identified as the Kondo resonance. We find that both the binding energy and width of this peak are significantly larger than theory predicts. It is also found that the trends in 4f line shape and surface shift between YbAl3 and LuAl3 are consistent with the trends seen between the 4f core levels of elemental Yb and Lu. Similar results are also found in YbCu2Si2 and YbAgCu4 for similar cycling methods. Recent observations of temperature dependence in these systems are most easily understood in terms of surface phenomena. © 1993 The American Physical Society.