Torsions as a new dynamic feature in 2D plasma crystals

Complex plasmas represent the plasma state of soft matter. They consist of a weakly ionized gas where small particles of solid matter are dispersed. Particles charge up and interact with each other through the screened Coulomb potential. They can form various ordered structures including monolayer (2D) crystalline lattices. As any kind of crystal, 2D plasma crystals support various collective excitations, some of them generic and others plasma-specic. Examples include phonons excited by particle thermal motion, hybrid modes generated by mode-coupling instability, and dislocations generated by excessive shear stress. In this presentation, we report on a new type of collective excitation in 2D plasma crystals, a spinning pair of particles, which we call a torsion. It is a dissipative structure where energy input is provided by the flow of ions and energy dissipation is through the neutral gas friction on particles. Non-reciprocal attraction between the particles in a torsion is due to the plasma wake effect