7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Screw dislocation dynamics in the transient relaxation of confined Yukawaliquids after quenching
Yun-Xuan Zhang, Hao-Wei Hu, Yi-Cheng Zhao, and Lin I
Department of Physics and Center for Complex Systems,
National Central University, Jhongli 32001, Taiwan
e-mail (speaker): yunxuanzhang1998@gmail.com
In confined liquids, flat boundaries can suppress thetransverse thermal motion of particles and induce layer
formation nearby the boundary, with thickness about thestructural correlation length of the bulk liquid. Throughquenching the system below the melting point, thelayering front can further invade the bulk liquid[1].
However, after the layers fully occupy the entire systemin the transient relaxation after quenching, layers are not
perfectly aligned. Thermal agitation can still generate
layer undulation and facilitate the formation of local
layering disorders in the system. Nevertheless, theirgeneric dynamical behaviors remain unknown.
Screw dislocations (SDs) are fundamental filamentlike defects with undefined phases winded around byhelical layered fronts. They are important phasesingularities commonly found in layered systems. For
example, the spontaneously generated chaotic SDs in thexyt space of self-excited dust acoustic waves have been
demonstrated experimentally, where xy plane is the plane
normal to the wave propagation direction. The modulation
instability leading to waveform undulation, rupture, andreconnection was found to be the key for SD generation[2].
Recent studies have also discovered SDs in macroscopic
layered structures like biomineralized nacre and blockcopolymer [3,4]. However, the generic behaviors of SDs andtheir dynamical evolutions in the xyz space remain elusive.
In this work, from the aspect of SDs dynamics, we
numerically investigate the evolution of local disorders ofconfinement-induced layering in the transient relaxationof Yukawa liquids after quenching below the layer
formation temperature, through Langevin-type molecular
dynamic simulation. Two flat boundaries normal to the zaxis act as topological constraints, making particles form
49 layers. It is found that, after layers fully extend over theentire system, pairs of SDs with opposite helicities can bespontaneously generated, in the form of chaotic filaments.
With increasing time after quenching. The small-scale
fluctuations of SDFs gradually decrease, leaving large SDloops or long SD strings still exhibiting slow temporalfluctuations. The basic generic SD dynamical processes
for SDF fluctuation, interaction, breaking-reconnection,etc., and their topological origins are classified anddiscussed. The constructed picture sheds light onunderstanding SD dynamics in other layered systems suchas nonlinear traveling wave systems. This work is
supported by the National Science and Technology
Council of Taiwan, under contract No. MOST-111-2112M-008-017.
References[1] W. Wang et al, Phys. Rev. Lett. 124 165001 (2020).
[2] Y. Y. Tsai et al, Nature Phys. 12 573 (2016).
[3] M. Beliaev et al, Nature Phys. 17 410 (2021).
[4] H. S. Kang et al, Sci. Adv. 8 eabm5120 (2022).

Figure 1. a, Typical side-view snapshot of the particle configuration with imperfect layering (circled region), in the lower
half of the thin vertical slab (3 a in thickness, where a is the mean distance of two adjacent intra-layer particles) normal
to the boundary, at a certain time after fully layering. Here, D for the vertical axis is the mean interlayer distance. b,Color-coded plots of the coarse-grained particle density n (left) and the corresponding phase ϕ (right) on the xy, xz, andyz planes. The crosses denote defect locations with undefined phases, located at the vertices of the pitchfork structure.
The defect position in the front xz plane corresponds to the center of the circled region in (a). c, Typical SDF configurationin the entire simulation box at the same time, showing the formation of SD loops (labeled by I to III).