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

TL;DR

This paper develops a microscopic Hamiltonian theory demonstrating that odd viscosity, a non-dissipative fluid property, exists in active matter systems in both 2D and 3D, revealing new effects like shear wave propagation.

Contribution

It provides the first microscopic theory for odd viscosity in active materials, extending its applicability to 3D and internally driven systems like living matter.

Findings

Odd viscosity exists in 3D active fluids.

Propagation of anisotropic shear waves due to odd viscosity.

Breakdown of Bernoulli's principle in systems with odd viscosity.

Abstract

In common fluids, viscosity is associated with dissipation. However, when time-reversal-symmetry is broken a new type of non-dissipative `viscosity' may emerge. Recent theories and experiments on classical 2D systems with active spinning particles have heightened interest in odd viscosity, but a microscopic theory for it in active materials is still absent. Here we present such first-principles microscopic Hamiltonian theory, valid for both 2D and 3D, showing that odd viscosity is present in any system, equilibrium or not, with aligned spinning components. Our work substantially extends the applicability of odd viscosity into 3D fluids, and specifically to internally driven active materials, such as living matter (e.g., actomyosin gels). We find intriguing 3D effects of odd viscosity such as propagation of anisotropic bulk shear waves and breakdown of Bernoulli's principle.