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DY: Fachverband Dynamik und Statistische Physik

DY 21: Active Matter 1 - organized by Carsten Beta (Potsdam), Andreas Menzel (Magdeburg) and Holger Stark (Berlin) (joint session DY/BP/CPP)

DY 21.1: Vortrag

Dienstag, 23. März 2021, 09:30–09:50, DYa

Swirl formation of active colloids near criticality — •Robert C. Löffler¹, Tobias Bäuerle¹, Mehran Kardar², Christian M. Rohwer³, and Clemens Bechinger¹ — ¹FB Physik, Universität Konstanz, Germany — ²Dep. Physics, MIT, Cambridge, MA, USA — ³Dep. Mathematics, University of Cape Town, South Africa

Animal groups like flocks of birds or schools of fish normally show a high degree of order. Yet they are also responsive to external factors in order to optimize nutrition and avoid predation. Various observations of such responsiveness have let to the assumption that those systems represent a state of order close to a critical point.

In our experiments, we use light-responsive active Brownian particles (ABPs) to which we can apply individual torques in a feedback controlled system to study such behavioral rules. Through the variation of a single parameter in our interaction model based on information about a particles local neighbors, we observe a continuous phase transition in the collective motion of the group: The ABPs transition from a disordered swarm to a stable swirl (i.e. milling, vortex-like state). Being able to continuously change our control parameter we observe a critical point with explicit bifurcation dynamics in the rotational order parameter and critical slowing down, as well as hysteresis in the symmetry-breaking regime of the control parameter. Observation of such critical behavior in simple models not only allows for more insight in complex animal behavior but also helps with designing future rules for collective tasks in robotic or other autonomous systems.

Bäuerle et al., Nat. Comm. 11, 2547 (2020); Löffler et al. (in review).