Slow Plastic Creep of 2D Dusty Plasma Solids

We report complex plasma experiments, assisted by numerical simulations, providing an alternative qualitative link between the macroscopic response of polycrystalline solid matter to small shearing forces and the possible underlying microscopic processes. In the stationary creep regime we have determined the exponents of the shear rate dependence of the shear stress and defect density, being $\alpha =1.15\pm 0.1$ and $\beta =2.4\pm 0.4$, respectively. We show that the formation and rapid glide motion of dislocation pairs in the lattice are dominant processes.

Figure 1

Scheme of the optical setup used to generate the wide shearing laser beams. Main parts: $L$, laser source (TEX, max 5.5 W @ 532 nm; BUD, max 1 W @ 440 nm); $G$, laser line generator lens; $C$, cylindric lens; $F$, linearly variable density filter.

Figure 2

Illustration of the data evaluation process for both experiments (left column, TEX; right column, BUD). For the unperturbed cases, (a) example of particle snapshots with the regions of interest, (b) pair correlation function, (c) defect maps (upper triangle, particle with seven neighbors; lower triangle, particle with five neighbors). (d) $v_x(y)$ transverse particle velocity profiles for different shearing laser powers.

Figure 3

Defect fraction (upper row) and shear stress (lower row) versus shear rate from both the TEX (left column) and BUD (right column) experiments. Lines are functional fits, see text.

Figure 4

Defect maps of subsequent system snapshots from the BUD experiment. Colors lighten with elapsing time. upper triangle, particles with seven neighbors; lower triangle, particles with five neighbors.

Figure 5

Computed shear stress (a) and defect fraction (b) versus shear rate for a set of homologous temperatures. The bounding dotted lines in (a) show simple power law functions with exponents as labeled.