Intermediate Valence Spectroscopy
Spectroscopic properties of intermediate valence compounds are studied using the Anderson model. Due to the large orbital and spin degeneracy Nf of the 4f-level, 1/Nf can be treated as a small parameter. This approach provides exact T = 0 results for the Anderson impurity model in the limit Nf→∞, and by adding 1/Nf corrections some properties can be calculated accurately even for Nf=1 or 2. In particular valence photoemission and resonance photoemission spectroscopies are studied. A comparison of theoretical and experimental spectra provides an estimate of the parameters in the model. Core level photoemission spectra provide estimates of the coupling between the f-level and the conduction states and of the f-level occupancy. With these parameters the model gives a fair description of other electron spectroscopies. For typical parameters the model predicts two structures in the f-spectrum, namely one structure at the f-level and one at the Fermi energy. The resonance photoemission calculation gives a photon energy dependence for these two peaks in fair agreement with experiment. The peak at the Fermi energy is partly due to a narrow Kondo resonance, resulting from manybody effects and the presence of a continuous, partly filled conduction band. This resonance is related to a large density of low-lying excitations, which explains the large susceptibility and specific heat observed for these systems at low temperatures.
KeywordsConduction State Core Hole Anderson Impurity Model Coulomb Matrix Element Folding Technique
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