Anisotropic shear melting and recrystallization of a two-dimensional complex (dusty) plasma

TL;DR

This study investigates how a two-dimensional plasma crystal responds to localized shear stress, revealing orientation-dependent melting, shear thinning behavior, and shear-induced particle reordering.

Contribution

It demonstrates the anisotropic response of plasma crystals to shear stress, including shear thinning and flow-induced particle alignment, which advances understanding of complex plasma rheology.

Findings

Shear melting depends on crystal orientation.

Shear viscosity exhibits minima in high shear regions.

Particles form flow-aligned strings during steady-state flow.

Abstract

A two-dimensional plasma crystal was melted by suddenly applying localized shear stress. A stripe of particles in the crystal was pushed by the radiation pressure force of a laser beam. We found that the response of the plasma crystal to stress and the eventual shear melting depended strongly on the crystal's angular orientation relative to the laser beam. Shear stress and strain rate were measured, from which the spatially resolved shear viscosity was calculated. The latter was shown to have minima in the regions with high velocity shear, thus demonstrating shear thinning. Shear-induced reordering was observed in the steady-state flow, where particles formed strings aligned in the flow direction.