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Condensed Matter Theory

Quantum Many-body Theory

The team of researchers around Professor Peter van Dongen (KOMET 337) investigates the physical properties of interacting quantum many-particle systems. The systems studied consist typically of either fermionic or bosonic particles, but, in principle, fermionic-bosonic mixtures are also of interest. Of particular interest to us are the properties of strongly correlated electron systems, since various important physical phenomena are caused by the strong electron-electron interaction in these materials. Examples of such phenomena are metal-insulator transitions, various types of magnetism, high-temperature superconductivity, the Kondo- and multichannel Kondo effects, the fractional quantum Hall effect, colossal magnetoresistance, formation of stripes, and electronic phase separation. In recent years the group also studied the physical properties of ultracold fermionic quantum gases in a harmonic trap, in particular their low-temperature phases with broken symmetries, such as superfluidity and antiferromagnetism.

These phenomena are described theoretically by effective quantum field theories, which are studied either analytically (perturbatively or through exact solutions) or numerically. The paradigm of such a quantum field theory is the so-called Hubbard model, which describes, in the simplest possible manner, both the kinetic energy and the interaction of fermionic particles on a lattice (e.g., of conduction electrons in narrow bands in solids). The most important numerical method, applied by us, is the Quantum Monte Carlo simulation, if necessary in combination with the Maximum Entropy method. Alternatively (or in addition) we also use numerics to solve equations, obtained from exact solutions or perturbation theory, or to calculate Feynman diagrams. Please feel free to surf around our site, if you wish. For comments or questions simply choose "contact"