Dislocation nucleation and motion observed in a 2D Yukawa triangular lattice

Dislocation nucleation and motion were studied experimentally in a 2D Yukawa triangular lattice. Edge dislocations were created in pairs in lattice locations where the internal shear stress exceeded a threshold and then moved apart in the glide plane at a speed higher than the sound speed of shear waves. The early stage of this process is identified as a stacking fault. At a later stage, supersonically moving dislocations generated shear-wave Mach cones. The experimental system, a plasma crystal, allowed observation of this process at an atomistic (kinetic) level. We used a monolayer suspension of microspheres in a plasma, i.e., a complex plasma, which is like a colloidal suspension, but with an extremely low volume fraction and a partially-ionized rarefied gas instead of solvent. At our experimental conditions, the suspension forms a highly ordered 2D triangular lattice. Dislocations were generated in this lattice due to the shear introduced by its differential rotation, with two ``rigid'' domain walls imbedded in it. We used digital video microscopy for direct imaging and particle tracking.