Dresden 2020 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 63: Active Matter IV (joint session DY/BP/CPP)

CPP 63.2: Talk

Wednesday, March 18, 2020, 10:15–10:30, ZEU 160

Swirl formation of active colloids near criticality — •Robert C. Löffler, Tobias Bäuerle, and Clemens Bechinger — Fachbereich Physik, Universität Konstanz, Konstanz D-78464, Germany

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. The propulsion applied to each ABP is thereby calculated based on information about its local neighbors. Through the variation of a single parameter in our interaction model, which is related to zonal models used in theoretical biology, 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 can also measure the susceptibility of the collective motion, peaking at a critical point within the transition. 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.

T. Bäuerle et al., Nat. Comm. 9, 3232 (2018); F. A. Lavergne et al., Science 364, 70-74 (2019).