| dc.description.abstract | Boundary surface induced layering occurs in many strongly coupled systems, such as colloids, metallic glasses, and dusty plasmas. The topological constraint from the boundary surface tends to line up particles, form layered structure and suppress particle trans-layer motions through mutual interaction. Thermal agitations tend to deteriorate structural order. Past studies mainly focused on layering formation and the associated dynamical slowing down in confined liquids, and the fractal like behavior of the layering front and the formation of different three dimensional (3D) crystalline ordered domains (CODs) after deep quenching. Nevertheless, the heterogeneous structural rearrangements of 3D CODs and their dynamical origins are open fundamental issues.
Microscopically, for the quenched 3D liquid under confinement, the layered region can be viewed as a 2+1D system composed of a stack of coupled 2D layers. Recent studies on 2D Yukawa liquids without confinement effect showed that the 2D cold liquid around freezing can be viewed as a patchwork of CODs with triangular lattice structure and different lattice orientations, which can be rearranged through rupturing/healing of CODs by thermally induced cooperative hopping. Nevertheless, comparing with 2D systems, in the layered region of the quenched 3D liquid, the interlayer coupling under various 3D COD structures can further complicate the intralayer structures and motions, which in turn affect the 3D COD structures and motions. Moreover, under the competition of thermal agitation and mutual interaction, the interface between the layered and unlayered regions might be a rough surface with various fluctuation scales.
Therefore, it is intriguing to unravel the following unexplored important issues. A) What are the spatiotemporal evolution and fluctuations of the layering front? B) In the layered region, what are the basic intralayer 2D structure and how does the local relative intralayer structures of adjacent layers affect the local 3D COD structures? C) What are the basic thermally excited intra- and interlayer cooperative motions, and how do they affect 3D COD structural rearrangement?
Here, these issues are experimentally addressed in a quenched 3D dusty plasma liquid by correlating with intra and interlayer motions. The topological constraint from the bottom sheath surface lines up the particles and induces layering. It is found that the scale free turbulent layering front first invades upward into the liquid region, and then fluctuates around a saturated level. The layered region can be viewed as a 2+1D system of vertically coupled layers exhibiting hexatic intra-layer structure with slow decay of long range triangular lattice order. The similar intralayer lattice orientations of adjacent layers with different horizontal shifts of intralayer lattice lines allow the formation of the 3D FCC, BCC, and HCP structures with specific lattice orientations vertical to the boundary. Particles in each layer alternatively exhibit heterogeneous thermally induced intralayer cooperative cage rattling and hopping. Heterogeneous cooperative motions of adjacent layers are the key for causing the interlayer sliding and leading to heterogeneous 3D structures and structural rearrangements. | en_US |