Dynamical Heterogeneities in 2D Dusty Plasma Liquids at the Discrete Level

Abstract

Down to the discrete microscopic level, the liquid is neither homogeneous nor completely disordered. The interplay of mutual coupling and thermal agitation makes the system support short range structural order, and avalanche-type cooperative hopping excitations which lead to structural arrangement. The rich dynamical behaviors of spatio-temporal heterogeneities are still poorly understood because of the lack of proper tools for direct visualization. The dusty plasma liquid can be self-organized by negatively charged micrometer sized dusts suspending in a low-pressure rf discharge background. Its sub-mm inter-particle distance and the tens of second thermal relaxation time make it a proper system to mimic and understand the generic spatio-temporal behaviors of the liquid at the discrete kinetic level through direct optical video-microscopy. In this paper, we briefly review the recent studies on the dynamical heterogeneities of the cold 2D dusty plasma liquids at the discrete level. The effects of mutual interaction, thermal agitation, external shear, and tight confinement on micro-motion, anomalous diffusion, avalanche-type excitations of hopping clusters and defect clusters, structural ordering and rearrangement, and visco-elastic responses are presented and discussed.

Cooperative microexcitations in 2+1D chain-bundle dusty plasma liquids

“…Similar to the 2D system, ordered domains with triangular lattice type structures, in which dusts exhibit caged oscillation, are surrounded by disordered regions with defects where dusts exhibit cooperative horizontal hopping and rearrange the microstructure. 14,16,17 Overlapping the dust trajectory plots of the above three different planes shows that the structures and motions for different layers are only similar in some regions ͓Fig. 2͑d͔͒.…”

“…[14][15][16] Previous studies showed that, in the horizontal ͑xy͒ plane, its structure has many small triangular lattice type ordered domains surrounded by defect clusters, similar to other 2D liquids. [14][15][16][17][18][19][20] The chains exhibit thermal induced stick-slip horizontal motion, with alternating small amplitude oscillation in the caging well formed by the nearest neighbors, and cooperative horizontal hopping over the caging barrier after accumulating sufficient constructive perturbations from thermal kicks and strain induced stress. [14][15][16] The hopping induces defect motion and structural rearrangement.…”

“…[14][15][16] The hopping induces defect motion and structural rearrangement. 16,19,20 For the cold liquid with long chains, chains are no longer stiff and become flexible. We still can expect the similar structure and motion in the xy plane to those of the 2D liquid, due to the horizontal caging by topological constraints from the neighboring chains.…”

“…The dynamics of chain motion and the correlation with structural order are important unexplored issues. The past works about the microdynamics of dusty plasma liquids are mainly limited to the quasi-2D liquid with short stiff unbreakable chains, [14][15][16] and the monolayer 2D liquid. 18 In this work, we experimentally study the above unexplored issues in the 2 + 1D dusty plasma liquid with long flexible chains using a scanning video dust-tracking system.…”

“…[14][15][16][17][18][19][20] The chains exhibit thermal induced stick-slip horizontal motion, with alternating small amplitude oscillation in the caging well formed by the nearest neighbors, and cooperative horizontal hopping over the caging barrier after accumulating sufficient constructive perturbations from thermal kicks and strain induced stress. [14][15][16] The hopping induces defect motion and structural rearrangement. 16,19,20 For the cold liquid with long chains, chains are no longer stiff and become flexible.…”