Zentralprojekt

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The fundamental understanding of the glass transition constitutes one of the grand challenges in Statistical Physics and Materials Science. It addresses slow cooperative processes in disordered systems where the mechanisms of particle rearrangements and transport are largely unknown. External fields have strong effects, as the time scales of external drive and intrinsic structural rearrangements can easily be made to match. External fields have significant effects on melt properties and the glass transition, and the investigation of the nonlinear response of supercooled liquids to controlled external fields will considerably contribute to our understanding of the complex underlying physics. External manipulations and processing also have an enormous technological impact, e.g., for the final solid properties. Supercooled liquids fall out of equilibrium by themselves upon lowering the temperature, and are also easily driven out of equilibrium by even slow quenches of external fields. Testing the nonlinear response in glassforming systems thus lies at the frontier of studying non-equilibrium and amorphous materials. Our research unit (RU) investigates the combined effects of strong external fields and slow cooperative dynamics in glass-forming systems in order to understand the complex structural, relaxational, and transport phenomena under conditions far from equilibrium. The RU uses strong mechanical and electric fields to obtain insights into the particle motion at the glass transition. Investigated materials range from supercooled alloys, colloidal dispersions, molecular glass formers to ionic fluids, granular media, and disordered media. Experimental techniques include mechanical, dielectric, and conductivity spectroscopy, while theoretical methods include variants of nonequilibrium computer simulations, mode coupling and kinetic theory, potential energy landscape, as well as continuous time random walk analysis. While in the first funding period of the RU common frameworks and approaches were developed for the joint investigations, in the second funding period the heterogeneous dynamics, the resulting length scales of heterogeneous transport, and the transient response under strong applied load or bias will be unifying themes of the continuing collaborations.