Microscopic dynamics in two-dimensional strongly-coupled dusty plasmas

A strongly-coupled plasma is a collection of free charged particles that interact with a Coulomb repulsion that is so strong that nearby particles do not easily move past one another. Unlike weakly-coupled plasmas, strongly-coupled plasmas exhibit a self-organization of particles into an arrangement like a solid crystalline lattice or a liquid. Dusty plasmas consist of micron-size particles of solid matter that are immersed in a plasma of electrons and ions. The dust particles gain a large electric charge and become strongly coupled. The motion of discrete particles can be tracked using a video microscopy diagnostic. Dusty plasma experiments allow a study of strongly-coupled plasma physics and an experimental simulation of condensed matter physics. Experiments are reported using a single layer of particles in the plasma to study two-dimensional (2D) physics. It is demonstrated experimentally that in addition to the solid and liquid states, a strongly-coupled dusty plasma can exist in an exotic state called a superheated solid. A 2D dusty plasma, initially self-organized in a crystalline lattice, is heated rapidly by rastered laser beams. The suspension remains in a solid lattice at a temperature well above the melting point. Shear-induced melting is studied in a 2D dusty plasma by applying shear to a crystalline lattice using a pair of oppositely-directed laser beams. Unexpectedly, coherent longitudinal waves are also excited in the resulting shear flow. In the first experiment of its kind, a suddenly-applied shear is found to produce a melting front that spreads at the transverse sound speed. The viscoelasticity of strongly-coupled plasmas in a liquid state is quantified. In the first experiment for any kind of physical system, the wavenumber-dependent