Strong Electronic Correlations and Low Energy Scales

One of the many fascinating aspects of strongly correlated electron systems is the appearance of low energy scales: interesting physical phenomena are observed on an energy (and temperature) scale much lower than e.g. local Coulomb repulsion, hybridization, etc. Well known examples are heavy fermion compounds and systems in the vicinity of a metal-insulator transition. These phenomena can be described using simple (but nevertheless strongly correlated) electronic models. For these models, the great difference in energy scales in general represents a difficult task for the theoretical investigation. The numerical renormalization group method turns out to be a very efficient tool to deal with these problems. This method was developed by Wilson for the investigation of the Kondo model and has been recently (successfully) applied to lattice models (such as Hubbard model and periodic Anderson model) within the dynamical mean field theory.