Nonequilibrium Phases of Living Chiral Fluid

Activity and chirality are fundamental properties both in living and synthetic active matter, breaking time-reversal symmetry and leading to novel material behavior and responses not seen in passive materials. Here, we will introduce the living chiral fluids formed by sea urchin embryos. Through detailed experimental characterization, we explore embryos' chiral activity and complex hydrodynamic interaction at the microscopic scale. Specifically, we examine pairs of embryos and find that the long-ranged anisotropic interaction promotes flock formation. Leveraging our experimental data, we perform numerical simulations and analytical theory to explore the diverse nonequilibrium phases across a wide parameter space. These phases are distinguished by order parameters such as correlation length and orientational order, revealing how collective patterns arise in chiral active fluids.