Complex plasma with Janus particles as a model active-matter system

Abstract

Active matter is a collection of active particles, each of which can extract energy from their environment and convert it into directed motion, thereby driving the whole system far from equilibrium. Janus particles have two halves of different properties. A two-dimensional complex plasma containing active Janus particles was studied experimentally. A single layer of micrometer-sized plastic microspheres coated on one side with a 10-nm layer of platinum was suspended in the plasma sheath above the lower electrode in a capacitively coupled radio-frequency low-pressure discharge in argon. When suspended in plasma, the Janus particles acquired self-propulsion and moved in characteristic looped trajectories suggesting a combination of spinning and circling motion; their suspension was in a highly disordered liquid state. We study various spatio-temporal correlations in this homogeneous isotropic active liquid state and discuss whether it has characteristics of active turbulence.