J.W. Allen

Valence fluctuations in narrow band oxides

Recent applications of the Anderson Hamiltonian in describing the electronic structure of narrow band oxides are described, using NiO, CeO2 and Ce2O3 as detailed examples. It is suggested that some transition metal compounds like NiS may be mixed valent in the true sense of having low-energy charge fluctuations.

Temperature-induced valence change of YbAl2 studied by XPS and BIS

Abstract The electronic structure of YbAl2 was studied by X-ray photoemission spectroscopy (XPS) and Bremsstrahlung Isochromat Spectroscopy (BIS) at three different temperatures. A change in valence from ≈ 2.3 at 120 K to ≈ 2.5 at 750 K was observed. The BIS spectra of YbAl2 show two peaks within 3 eV of the Fermi level, although the origin of the second peak is not clear.

Electron spectroscopy study of the heavy Fermion compound URu2Si2

Abstract We report x-ray photoemission, resonant photoemission and bremsstrahlung isochromat spectra of the 4f core levels, the valence band and the conduction band, respectively, of the heavy fermion compound URu 2 Si 2 . The resonant photoemission behavior of the uranium 5f weight resembles that of cerium 4f weight in that the portion away from the Fermi energy has a delayed resonance relative to that at the Fermi energy. We also assess current efforts to interpret uranium spectra.

Intrinsic surface binding energy shifts in Yb metal

Abstract We report on the four-peak structure observed in the region of 4 f photoemission in Yb metal, using synchrotron radiation in the energy range 70–200 eV. We conclude, contrary to previous reports, that the doublet associated with surface emissions results from an intrinsic surface shift on clean regions of the surface. We also demonstrate that the observed structure is consistent with earlier XPS measurements, and we set an upper limit on the width of the bulk peaks.

Valence-band densities of state in NiAs

Abstract Valence-band resonant photoemission data on NiAs are compared to corrected linear muffin-tin orbital (LMTO) density-of-state (DOS) calculations. The observed bandwidth is 6 eV with the main Ni 3d peak at 1.8 ev below the Fermi edge and shoulder ∼1 eV wide at E F , in agreement with the calculated Ni d-projected DOS.

Electron spectroscopy study of the heavy fermion compound U2Zn17

Abstract We report X-ray photoemission, resonant photoemission and Bremsstrahlung isochromat spectra of the 4f core levels, the valence band and the conduction band, respectively, of the heavy fermion compound U 2 Zn 17 and the reference compound Th 2 Zn 17 , and we assess current efforts to interpret such spectra.

ELECTRON SPECTROSCOPY AND THE KONDO VOLUME COLLAPSE IN Ce0.7Th0.3

Abstract An electron spectroscopy study of the continuous α-γ transition in Ce 0.7 Th 0.3 has been made for temperatures between 100 and 310 K. A rough analysis of the results shows qualitative agreement with the Kondo Volume Collapse model, as derived from the Anderson Hamiltonian.

Low temperature properties of CeIr3B2 and Ulr3B2

Abstract The compounds CeIr 3 B 2 and UIr 3 B 2 have been investigated at low temperatures by means of electrical resistivity ϱ, dc magnetic susceptibility and specific heat measurements. The ϱ vs. temperature curves for both compounds are reminiscent of valence fluctuation or Kondo lattice behavior. Resonant photoemission data are presented for UIr 3 B 2 .

Resonance Effects in the Valence-Band Spectra of Yb2O3

Resonance effects at the 4d threshold of rare-earths and rare-earth compounds are well-established in absorption spectra. In this paper we present experimental results for studies of the decay processes following the absorption in a model system, namely Yb2O3, where the 4f occupancy is 4f13 and where the 4d → 4f absorption thus produces a single resonance peak.