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DY: Fachverband Dynamik und Statistische Physik
DY 12: Posters DY - Fluid Physics, Active Matter, Complex Fluids, Soft Matter and Glasses (joint session DY/BP)
DY 12.18: Poster
Monday, March 22, 2021, 14:00–16:30, DYp
Bistable vortices formed by active particles with retarded interactions - Theory — Xiangzun Wang1, •Pin-Chuan Chen2, Viktor Holubec2,3, Klaus Kroy2, and Frank Cichos1 — 1Molecular Nanophotonics Group, Peter Debye Institute for Soft Matter Physics, University of Leipzig, 04103 Leipzig — 2Institute for Theoretical Physics, University of Leipzig, 04103 Leipzig, Germany — 3Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, 18000 Prague, Czech Republic
In a recent experiment (see the companion contribution ``Experiment'', serial number DY193), thermophoretic microswimmers were observed to self-assemble into a bistable mode of circular collective motion. We explain the underlying mechanism qualitatively by deriving a coarse-grained Langevin model for active Brownian particles with retarded interactions. For a single microswimmer attracted to an immobile attractive sphere, it can be broken down to an effective model for the angular degree of freedom. The reduced one-dimensional overdamped Langevin equation features a virtual potential for the angular velocity, self-generated by the retarded propagation of the interaction. We work out the quantitative analytical predictions for the delay-dependent bifurcation scenario and the Kramers rates and numerical results for spontaneous transitions between the degenerate chiral modes of angular motion, beyond the bifurcation point. Our theoretical predictions are found to agree well with the experimental observations and simulations.