Electron correlations in systems with orbital degeneracies: The dual nature of 5f electrons, heavy fermions and spectral functions in U-compounds

The present paper focuses on the dual nature of 5f electrons in U compounds and the concept of partial localization. The latter can arise due to intra-atomic correlations described by Hund's rules. To derive a microscopic picture, the electronic correlations in orbitally degenerate systems are studied by exact diagonalizations for finite clusters. Results for excitation spectra are presented. The cluster calculations form the basis for an approximate treatment of extended systems. The excitation spectra of U-based compounds are calculated for models which account for the local atomic correlations and realistic band structures. We discuss how high-energy shoulders observed in photoemission can be understood and how heavy fermions can emerge.     «

The present paper focuses on the dual nature of 5f electrons in U compounds and the concept of partial localization. The latter can arise due to intra-atomic correlations described by Hund's rules. To derive a microscopic picture, the electronic correlations in orbitally degenerate systems are studied by exact diagonalizations for finite clusters. Results for excitation spectra are presented. The cluster calculations form the basis for an approximate treatment of extended systems. The excitation...     »