Multi-orbital Anderson models and the Kondo effect: a NCA study enhanced by vertex corrections
Institut für Festkörperphysik, Technische Universität Darmstadt, Hochschulstr. 6, 64289 Darmstadt, Germany
Corresponding author: a firstname.lastname@example.org
Revised: 16 January 2008
Published online: 28 February 2009
The low energy region of certain transition metal compounds reveals dramatic correlation effects between electrons, which can be studied by photoelectron spectroscopy. Theoretical investigations are often based on multi-orbital impurity models, which exhibit modified versions of the Kondo effect. We present a systematic study of a multi-orbital Anderson-like model, based on a new semi-analytical impurity solver which goes beyond simple modifications of the well known NCA. We discuss one-particle excitation spectra and in particular the role of level positions and Coulomb-matrix elements. It is shown that the low-energy region as well as the overall features of spectra critically depend on the model parameters and on the quality of the approximations used. Recent photoelectron experiments and corresponding existing calculations are put into perspective. An interesting crossover scenario between different regimes of ground states with characteristically different local correlations is uncovered.
PACS: 71.10.-w – Theories and models of many-electron systems / 71.20.-b – Electron density of states and band structure of crystalline solids / 71.27.+a – Strongly correlated electron systems; heavy fermions / 71.55.-i – Impurity and defect levels
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2009