Topological waves in active fluids

Active fluids are composed of self-driven microbots that endow the liquid with a unique set of mechanical characteristics. I will present two designs for acoustic metamaterials exhibiting topological states: one using periodic confinement of an active liquid 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 rotating fluid as a result of the Coriolis force that breaks Galilean invariance and opens a gap at low frequency. I will explore how the number and spatial profile of topological edge states depends on an anomalous response coefficient called odd (or Hall) viscosity. As the sign of odd viscosity changes, a topological phase transition occurs without closing the bulk band gap.

References:

[1] A. Souslov, K. Dasbiswas, M. Fruchart, S. Vaikuntanathan, and V. Vitelli. Topological Waves in Fluids with Odd Viscosity. Phys. Rev. Lett. 122, 128001 (2019).

[2] A. Souslov, B. C. van Zuiden, D. Bartolo, V. Vitelli. Topological sound in active-liquid metamaterials. Nature Physics 13, 1091 (2017)