The research field of the 1st Institute for Theoretical Physics is the theory of condensed matter. The activities cover a wide spectrum ranging from the investigation of fundamental problems concerning the description of systems of interacting particles to more application-oriented questions. The variety of analytical and numerical methods employed is thus correspondingly large.
The investigation of strongly interacting many-body systems in which the primary concerns are the superconducting and magnetic phase transitions in a variety of crystal structures, continues to be a lively and timely research activity. However, in more recent years the focus of our scientific work has shifted increasingly towards systems with reduced dimensions and their unusual physical properties. This is the domain of mesoscopic physics where the size and the shape of the system play special roles. The application of methods developed in quantum field theory to such systems is often not practical. Since these methods are usually based on perturbation theory they are only conditionally applicable when interaction effects dominate over the ''free-particle'' properties. This is the case, for example, when the density of charge carriers is smaller than in typical metals. This occurs in many mesoscopic systems and also in the high temperature superconductors. The study of such highly correlated systems increasingly requires the use of numerical algorithms.
The investigation of macroscopic systems remains interesting due to the continual discovery of new materials with surprising and potentially very useful properties. Mesoscopic physics has moved into the limelight since, on the one hand, completely new physical effects have been discovered in low dimensional systems, and, on the other hand, small systems can be ''made to order'', often strongly motivated by potential applications.
The diversity of physical systems and the wide range of quite different investigational techniques insures that the education of diploma students and young scientists occurs in a modern research and application environment that proveides excellent perspectives for the future. The scientific activities of the Institute are integrated in the international research community through numerous worldwide partnerships.