Odd viscosity in active materials: microscopic origin and 3D effects

Active materials are composed of many components that convert energy from the environment into directed mechanical motion, thus locally breaking time reversal symmetry (TRS). Examples of active materials go beyond living systems such as bacteria and is also realized in e.g. colloidal rollers. A striking phenomenon of breaking TRS is the possible appearance of odd viscosity. Onsager reciprocal relations require that when TRS holds the viscosity tensor is symmetric for exchanging its first and last pair of indices. However, when TRS is broken, Onsager relations predict an odd viscosity that is both odd under TRS and under the change of indices. Such odd viscosity is non-dissipative and should thus be derivable from a Hamiltonian theory. Active materials innately break TRS, which led to recent studies of odd viscosity in 2D active materials. In this talk I will present a novel microscopic Hamiltonian theory for odd viscosity, valid also in 3D. Our theory give rise to intriguing 3D effects such as generalization of Bernoulli’s principle, propagation of bulk waves, and a few types of unidirectional surface waves. We further predict that odd viscosity should emerge in actomyosin gels and bacterial suspensions.