Spontaneous shock waves in pulse-stimulated flocks of Quincke rollers

Bo Zhang; Andreas Glatz; Igor S Aranson; Alexey Snezhko

doi:10.1038/s41467-023-42633-4

Spontaneous shock waves in pulse-stimulated flocks of Quincke rollers

Nat Commun. 2023 Nov 3;14(1):7050. doi: 10.1038/s41467-023-42633-4.

Authors

Bo Zhang^{1

2}, Andreas Glatz^{3

4}, Igor S Aranson^{5

6

7}, Alexey Snezhko⁸

Affiliations

¹ Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA. bz@nju.edu.cn.
² Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructure, and Department of Physics, Nanjing University, Nanjing, 210093, China. bz@nju.edu.cn.
³ Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA.
⁴ Department of Physics, Northern Illinois University, DeKalb, IL, 60115, USA.
⁵ Department of Biomedical Engineering, Pennsylvania State University, University Park, PA, 16802, USA.
⁶ Department of Chemistry, Pennsylvania State University, University Park, PA, 16802, USA.
⁷ Department of Mathematics, Pennsylvania State University, University Park, PA, 16802, USA.
⁸ Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA. snezhko@anl.gov.

Abstract

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.