title: Self-induced polar order of active Brownian particles in a harmonic trap.
abstract: Hydrodynamically interacting active particles in an external harmonic potential form a self-assembled fluid pump at large enough Péclet numbers. Here, we give a quantitative criterion for the formation of the pump and show that particle orientations align in the self-induced flow field in surprising analogy to ferromagnetic order where the active Péclet number plays the role of inverse temperature. The particle orientations follow a Boltzmann distribution Φ(p) ∼ exp(Ap(z)) where the ordering mean field A scales with the active Péclet number and polar order parameter. The mean flow field in which the particles' swimming directions align corresponds to a regularized Stokeslet with strength proportional to swimming speed. Analytic mean-field results are compared with results from Brownian dynamics simulations with hydrodynamic interactions included and are found to capture the self-induced alignment very well.
authors: Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany.
authors: Marc
authors: M
authors: Hennes
authors: Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany.
authors: Katrin
authors: K
authors: Wolff
authors: Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany.
authors: Holger
authors: H
authors: Stark
mesh_terms: D003102:Colloids / Q000737:chemistry; D057446:Hydrodynamics; D008954:Models, Biological; D008956:Models, Chemical; D008962:Models, Theoretical; D013550:Swimming
chemical_list: D003102:Colloids