Spontaneous self-excited odd elastic waves in living crystals*

When chiral active particles interact with each other non-reciprocally and form a crystal, the displacement gradient and the stress that were independent in passive materials become coupled. The resulting asymmetric off-diagonal elements in the elastic moduli tensor represent odd elasticity. The living crystal of embryos of starfish Patiria miniata has recently been shown to exhibit odd elasticity, with the possible indirect observation of odd elastic wave. However, simple models for odd elastic waves are overdamped because of viscous forces arising from the longitudinal interaction among the embryos. In this work, we show how to detect odd elastic waves by measuring appropriate current correlation functions. Analysis of the experimental data using the current correlation function approach demonstrates that the oscillatory behavior experimentally observed in the living crystal was self-circling motion of the embryos. Nevertheless, we show that noise can excite the wave despite the presence of damping, and discuss the conditions required for the observation of a stochastic odd elastic wave in this system.

This work was partially supported by the National Science Foundation under Grant no. DMR-2006446.