Active Matter that Flocks and Jams

The field of active matter has attracted a lot of attention due to the wealth of collective phenomena encountered in active systems. Among them, the most studied are likely the transition to collective motion that emerges from alignment between active particles [1] and the phase separation induced by repulsive forces, named Motility-Induced Phase Separation [2]. While these phenomena have been studied extensively separately, their interplay has only been studied little, even though both interactions are generically present in dense active systems. Motivated by experiments on self-propelled Quincke rollers [3], we combine numerical simulations and theory to characterize the phases that these interactions induce together. Our results reveal a rich phenomenology, which exceeds what has already been observed experimentally, and includes a stable triple-phase coexistence region in single-component active fluids.

[1] T. Vicsek, A. Czirók, E. Ben-Jacob, I. Cohen, and O. Shochet, Phys. Rev. Lett. 75, 1226 (1995), URL https://link.aps.org/doi/10.1103/PhysRevLett.75.1226.

[2] M. E. Cates and J. Tailleur, Annual Review of Condensed Matter Physics 6, 219 (2015), ISSN 1947-5462, URL https://www.annualreviews.org/content/journals/10.1146/annurevconmatphys-031214-014710.

[3] D. Geyer, D. Martin, J. Tailleur, and D. Bartolo, Phys. Rev. X 9, 031043 (2019), URL https://link.aps.org/doi/10.1103/PhysRevX.9.031043.