Compact dislocation clusters in a two-dimensional highly ordered complex plasma

Abstract

The mechanism and physics of defect nucleation are key questions that often remain open irrespective of the suggested melting scenario or the shear instability mechanism. Complex plasmas can serve as a powerful tool, providing a fundamental insight into the nucleation process generically. Either deformation-induced or thermally initialized nucleation in hexagonal plasma crystals starts with the appearance of compact dislocation clusters having a tetragon in the core. Hence, the competition for the minimal energy configuration between (stable) hexagonal symmetry and (unstable) tetragonal symmetry can be resolved in favor of a (meta-stable) ‘mixed symmetry’—a cluster of coupled dislocations in a hexagonal environment. Performing simulations with a specially designed tool—a deformable simulation cell—the mechanism of nucleation in two-dimensional plasma crystals is studied. The nontrivial topology of the dislocation clusters is explored in detail, and the results obtained agree well with experimental observations.