Active Fluids as Topological Metamaterials: Structure Without H Periodic Order

Abstract

Active liquids are composed of self-driven microbots that endow the liquid with a unique set of mechanical characteristics. We present two designs for topological states using active fluids: one using periodic confinement and another using a bulk fluid without periodic order. In a periodic lattice, geometry of confinement controls the structure of topological waves. Without periodic order, topological edge waves can arise in a fluid of self-spinning particles undergoing spontaneous active rotation. This can occur because a fluid undergoing rotation experiences a Coriolis force that breaks Galilean invariance and opens a gap at low frequency. Alternatively, such edge waves can arise due to a Lorentz force in a magnetized plasma. We explore the interplay of topological states and an anomalous response coefficient called odd (or Hall) viscosity. For large odd viscosity, this transverse response can be measured via the profile shape of topologically robust edge waves.