Phase Diagram of Active Brownian Spheres: Crystallization and the Metastability of Motility-Induced Phase Separation

Motility-induced phase separation (MIPS), the phenomenon in which purely repulsive active particles undergo a liquid-gas separation, is among simplest and most widely studied examples of nonequilibrium transition. Here, we show that states MIPS coexistence are fact only metastable for three-dimensional Brownian over very broad range conditions, decaying at long times through an ordering transition call crystallization. At activity just above critical point, binodal superseded by crystal-fluid curve, with solid, liquid, gas all coexisting triple point where two curves intersect. Nucleating crystal from disordered fluid, however, requires rare fluctuation exhibits nearly close-packed density solid phase. The corresponding barrier to crystallization surmountable on feasible timescale high activity, fluid densities near maximal packing. glassiness expected such dense liquids equilibrium strongly mitigated forces, so lifetime declines steadily increasing manifesting simulations as facile spontaneous extremely activity.Received 20 December 2020Revised 6 March 2021Accepted 5 April 2021DOI:https://doi.org/10.1103/PhysRevLett.126.188002© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCrystallizationNucleationPhase diagramsPhysical SystemsActive matterNonequilibrium systemsPolymers & Soft Matter