title: Negative Interfacial Tension in Phase-Separated Active Brownian Particles.
abstract: We study numerically a model for active suspensions of self-propelled repulsive particles, for which a stable phase separation into a dilute and a dense phase is observed. We exploit the fact that for nonsquare boxes a stable "slab" configuration is reached, in which interfaces align with the shorter box edge. Evaluating a recent proposal for an intensive active swimming pressure, we demonstrate that the excess stress within the interface separating both phases is negative. The occurrence of a negative tension together with stable phase separation is a genuine nonequilibrium effect that is rationalized in terms of a positive stiffness, the estimate of which agrees excellently with the numerical data. Our results challenge effective thermodynamic descriptions and mappings of active Brownian particles onto passive pair potentials with attractions.
authors.affiliation: Institut für Theoretische Physik II, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany.
authors.forename: Julian
authors.initials: J
authors.lastname: Bialké
authors.affiliation: Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany.
authors.forename: Jonathan T
authors.initials: JT
authors.lastname: Siebert
authors.affiliation: Institut für Theoretische Physik II, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Löwen
authors.affiliation: Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Speck