Topology in Polar Flocking and Active Nematics

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Author(s)
Bowick, Mark
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http://hdl.handle.net/1853/59691
Abstract
Active flocking on curved surfaces, such as the 2-sphere and the catenoid, exhibits dynamical symmetry breaking in the form of spontaneous flow, calculable inhomogeneous density patterns and long-wavelength propagating sound modes that get gapped by the curvature of the underlying substrate. Curvature and active flow together result in symmetry-protected topological modes that get localized to special geodesics on the surface. These modes are the analogue of edge states in electronic quantum Hall systems and provide unidirectional channels for information transport in the flock, robust against disorder and backscattering. Active nematics instead exhibit spontaneous motility of strength +1/2 disclinations and active torques that favor the motility-driven unbinding of defects. Despite the directed motion of defects, nematic order is stabilized by rotational noise at low enough activity. Within a perturbative treatment, active forces lower the effective defect-unbinding transition temperature.
Sponsor
Georgia Institute of Technology. College of Sciences
Georgia Institute of Technology. Institute for Materials
Georgia Institute of Technology. Parker H. Petit Institute for Bioengineering and Bioscience
Georgia Institute of Technology. School of Materials Science and Engineering
Georgia Institute of Technology. School of Physics
American Physical Society
Exxon Mobil Corporation
National Science Foundation (U.S.)
Date
2018-04-18
Extent
41:56 minutes
Resource Type
Moving Image
Resource Subtype
Lecture
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