Emergence of dynamic vortex glasses in disordered polar active fluids

Abstract

Significance Active systems, from bacteria to human crowds, often move through disordered environments, but the impact of quenched disorder on self-organized collective flow remains largely unexplored. We combine microfluidic experiments involving a colloidal active fluid and hydrodynamic theory to study a flocking fluid navigating a disordered substrate. While weak disorder hardly disrupts the robust collective motion, above a critical disorder strength the system organizes in a remarkable state of correlated flows through a frozen network of defects—a dynamical vortex glass, akin to vortex glasses in dirty superconductors. Strong disorder and activity conspire to generate a gauge field that proliferates pinned vortices, a general mechanism that may apply to a broad class of synthetic and biological active fluids. In equilibrium, disorder conspires with topological defects to redefine the ordered states of matter in systems as diverse as crystals, superconductors, and liquid crystals. Far from equilibrium, however, the consequences of quenched disorder on active condensed matter remain virtually uncharted. Here, we reveal a state of strongly disordered active matter with no counterparts in equilibrium: a dynamical vortex glass. Combining microfluidic experiments and theory, we show how colloidal flocks collectively cruise through disordered environments without relaxing the topological singularities of their flows. The resulting state is highly dynamical but the flow patterns, shaped by a finite density of frozen vortices, are stationary and exponentially degenerated. Quenched isotropic disorder acts as a random gauge field turning active liquids into dynamical vortex glasses. We argue that this robust mechanism should shape the collective dynamics of a broad class of disordered active matter, from synthetic active nematics to collections of living cells exploring heterogeneous media.