# Condensed-Matter Theory, Statistical and Computational Physics

The general goal of this research theme is to obtain a fundamental understanding of macroscopic phenomena on the basis of microscopic many-body theories. Within the theme a division can be made into topics that are intrinsically of a quantum-mechanical nature and topics that require only classical theory. The former include the quantum-Hall effects, superconductivity and superfluidity, Bose-Einstein condensation, quantum magnetism and quantum computation. The latter are, among others, the relationship between chaos and transport, granular matter, crystal surfaces, polymer dynamics, disordered materials, colloidal suspensions and liquid crystals.

The theme thus covers a large number of research topics. It shows a strong cohesion, because in all cases we deal with a many-body system of which the microscopic details are known and the macroscopic properties are to be determined. As a result mean-field theory, renormalization-group theory, and the scaling theory of critical phenomena play a central role. Moreover, in many cases not only the static or equilibrium behaviour of the system is of interest, but also its dynamical properties. Determining these requires the use of the sophisticated and rather universal methods of nonequilibrium statistical physics. Some examples are kinetic theory and the theory of stochastic processes.

As can be expected in theoretical condensed-matter and statistical physics, there are many contacts with experimental physics. These include explanations of existing experiments, predictions for possible new experiments, and explorations of properties of theoretical models that share essential features with experimental systems. However, direct contact with experiments can usually only be made after the theory has been tailored to the specific details of the experiment of interest. This often requires numerical means at some stage. Therefore, closely related numerical methods are used to explore the physical consequences of the theories used in regimes which are most relevant to experiment and where analytical means are often no longer adequate. Sometimes this requires the development of new computational techniques.