High Energy Spectroscopies
In the past ten years the so-called high energy spectroscopies have had a major impact on the understanding of the electronic structure of narrow-band systems. These spectroscopies have been used to determine the occupations, valence states and spectral weight distributions of the narrow band electronic states in question, 3d for transition metals, 4f for rare earths, or 5f for actinides. It is found that the spectra show systematic differences from the results of solid state local density functional calculations and thereby reveal the presence of the large Coulomb interactions in these systems. For pure transition metals1,2 and some metallic transition metal compounds,2,3 the spectra have been modeled with some success by the Hubbard Hamiltonian. For the rare earths4 and certain insulating transition metal compounds,2,5–11 the spectra can be described quite well by the impurity Anderson Hamiltonian, and if the Hamiltonian parameters thus obtained are used to evaluate quantities of significance for the low energy properties of the system, such as characteristic energies for loss of magnetic moments,4 or for magnetic ordering9, the results are in reasonable agreement with the values obtained directly from low energy experiments.
KeywordsCore Hole Transition Metal Compound Rare Earths4 Kondo Resonance Superconducting Copper Oxide
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