Surprises in Correlated Electron Physics

The exceptional properties of strongly correlated electron systems have fascinated physicists for several decades already [1–9]. New correlated electron materials and unexpected correlation phenomena are discovered every year. Often the properties of those systems are influenced by disorder. Unfortunately, real materials and even model systems with strong electronic correlations and disorder are notoriously hard to investigate theoretically because standard approximations are invalid in the most interesting parameter regime — that of intermediate coupling. Here the recently developed dynamical mean-field theory (DMFT) [10–17] has proved to be an almost ideal mean-field approximation since it may be used at arbitrary coupling. For this reason the DMFT has been successfully employed in the investigation of electronic correlation effects in theoretical models and even real materials [10–19]. The investigations of electronic correlations and their interplay with disorder by means of the DMFT has led to the discovery of several unexpected properties and phenomena. Examples are: (i) a purely electronic mechanism leading to kinks