Supersonic kinks and solitons in active solids

To show that steadily propagating nonlinear waves in active matter can be driven internally, we develop a prototypical model of a topological kink moving with a constant supersonic speed. We use a model of a bi-stable mass-spring (FPU) chain capable of generating active stress. In contrast to subsonic kinks in passive bi-stable chains, that are necessarily dissipative, the obtained supersonic solutions are purely anti-dissipative. Our numerical experiments point towards stability of the obtained kink-type solutions and the possibility of propagating kink-anti-kink bundles reminiscent of solitons. We show that even the simplest quasi-continuum approximation of the discrete model captures the most important features of the predicted active phenomena.