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DY: Fachverband Dynamik und Statistische Physik

DY 30: Statistical Physics far from Thermal Equilibrium

DY 30.1: Hauptvortrag

Mittwoch, 3. April 2019, 10:00–10:30, H6

Fluctuations and responses in nonequilibrium fluids — •Matthias Krüger — Institut für Theoretische Physik, Georg-August-Universität Göttingen

Understanding systems far from equilibrium is of fundamental and technological interest. The linear response of systems mildly perturbed from equilibrium can be understood in terms of the well known fluctuation-dissipation-theorem (FDT). Further away from equilibrium, the situation is generally less clear, and is the topic of manifold ongoing investigations.

We derive a path-integral version of nonlinear response theory, which can be considered an extension of the FDT to nonlinear responses, and discuss the fundamental properties of such extensions in relation to the FDT itself, and also test it experimentally in a colloidal model system.

These path integral techniques can also be used to derive Langevin-descriptions for nonlinear fluids, necessary for understanding the motion of (driven) probe particles in (nonlinear) viscoelastic surroundings; Indeed, due to the nonlinear responses of viscoelastic solvents (such as shear thinning behavior), a driven colloidal particle can display pronounced nonequilibrium fluctuations already at slow driving speeds, as will be demonstrated using recent experimental data.