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Dynamics of Complex Systems - Research Topics
 | Amorphous Solids Several glasses are being investigated with a variety of different experimental techniques in a wide range of frequencies and temperatures. Currently, the main focus lies on the question of the relevance of mutual interaction between tunneling states that may lead to interesting collective phenomena. Measurements of the dielectric constant, dielectric echo experiments and investigations of the elastic properties are being carried out . | |
 | Crystalline Defect Systems Certain point defects in crystals have several energetically degenerate positions between which they can tunnel even at very low temperatures. We study substitutional defects in alkali halide crystals with various dielectric methods to investigate the influence of interaction between the tunneling centers onto their dynamics in such well-characterized model systems. By doping the crystals with different amounts of defects, the number density and thus the mean interaction energy can be varied over a wide range. Measurements of the dielectric susceptibility are performed at frequencies 100 Hz - 6 GHz and at temperatures 5 mK - 300 K. In addition, polarization echos are investigated to study the phase coherence of the tunneling systems . | |
 | Condensed Films Noble gas films prepared by quench-condensation on a cold substrate exhibit a high degree of disorder; mixtures of different noble gases may even become amorphous. Such films are a model system for structural glasses since the interaction between the atoms is very simple and since their masses, radii, and binding energies can be varied over a wide range by using several sorts of noble gases. The elastic properties of noble gas films are investigated using surface acoustic waves and low-frequency mechanical oscillators . | |
 | Glass Transition It is largely unknown why some materials form a glass and others crystallize. Usually glasses are formed by quenching a liquid. We apply hydrostatic pressure in addition to arrive in the glassy state on an isothermal or isochoric path. Using dielectric and dilatometric methods we study the dynamics and statics at the glass transition and in the glassy state in dependence of the thermodynamic path. | |
