Zhang Bo, Glatz Andreas, Aranson Igor S, Snezhko Alexey
Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA.
Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructure, and Department of Physics, Nanjing University, Nanjing, 210093, China.
Nat Commun. 2023 Nov 3;14(1):7050. doi: 10.1038/s41467-023-42633-4.
Active matter demonstrates complex spatiotemporal self-organization not accessible at equilibrium and the emergence of collective behavior. Fluids comprised of microscopic Quincke rollers represent a popular realization of synthetic active matter. Temporal activity modulations, realized by modulated external electric fields, represent an effective tool to expand the variety of accessible dynamic states in active ensembles. Here, we report on the emergence of shockwave patterns composed of coherently moving particles energized by a pulsed electric field. The shockwaves emerge spontaneously and move faster than the average particle speed. Combining experiments, theory, and simulations, we demonstrate that the shockwaves originate from intermittent spontaneous vortex cores due to a vortex meandering instability. They occur when the rollers' translational and rotational decoherence times, regulated by the electric pulse durations, become comparable. The phenomenon does not rely on the presence of confinement, and multiple shock waves continuously arise and vanish in the system.
活性物质表现出在平衡状态下无法实现的复杂时空自组织以及集体行为的出现。由微观昆克滚轮组成的流体是合成活性物质的一种常见实现方式。通过调制外部电场实现的时间活动调制是扩展活性系综中可及动态状态种类的有效工具。在此，我们报告了由脉冲电场激发的相干运动粒子组成的冲击波模式的出现。冲击波自发出现且移动速度比平均粒子速度快。结合实验、理论和模拟，我们证明冲击波源于由涡旋蜿蜒不稳定性导致的间歇性自发涡旋核。当由电脉冲持续时间调节的滚轮平移和旋转退相干时间变得可比时，就会出现冲击波。该现象不依赖于限制条件的存在，并且系统中会不断出现和消失多个冲击波。
