Rapid phase transition in 2D active pseudocrystals

Abstract Active matter with continuous energy injection that exhibits various nonequilibrium emergent behaviors, such as swarming and motility induced phase separation, has been extensively studied in the past decades. Achieving desired patterns and phases in fabricating functional materials by assembling active matter is a rising and challenging direction. Nevertheless, the ossibility of a stably ordered structure of active matter remains elusive. Toward this goal, the interplay between the active force and the volume exclusion provides a new way to manipulate mechanical stability. Here, we demonstrate a new type of active, two dimensional (2D) pseudocrystal system consisting of arrays of active rods. The pseudocrystals with tetratic array demonstrate robust stability against the thermal noise. Increasing the active force leads to a phase transition from pseudocrystal to swarming via shear melting. In the traveling pseudocrystals, on the contrary, the synchronized movement of active rods reduces internal stresses and enhances the stability of pseudocrystals. Topological defects quickly propagate in the traveling pseudocrystals and assist the stability. The present framework provides innovative insights into potentially new designs and manipulations of active materials. PACS numbers: