  Non-equilibrium dynamics of topological defects can be used as a fundamental
propulsion mechanism in microscopic active matter. Here, we demonstrate
swimming of topological defect-propelled colloidal particles in (passive)
nematic fluids through experiments and numerical simulations. Dynamic swim
strokes of the topological defects are driven by colloidal rotation in an
external magnetic field, causing periodic defect rearrangement which propels
the particles. The swimming velocity is determined by the colloid's angular
velocity, sense of rotation and defect polarity. By controlling them we can
locomote the particles along different trajectories. We demonstrate scattering
-- that is, the effective pair interactions -- of two of our defect-propelled
swimmers, which we show is highly anisotropic and depends on the microscopic
structure of the defect stroke, including the local defect topology and
polarity. More generally, this work aims to develop biomimetic active matter
based on the underlying relevance of topology.
