Multistability in Non Reciprocal Metamaterial

Active metamaterials that break reciprocity and exhibit nonlinear mechanics can host novel spatiotemporal patterns. Here, we demonstrate multistability of travelling kinks and stripe states in a one-dimensional array of interconnected bistable elastic units driven by programmable internal torques. By combining non-reciprocal torque response with the intrinsic bistability of buckling beams and imposing geometric frustration via periodic boundary conditions, we engineer a topologically protected travelling kink. Experimentally, we observe a transition from static Peierls–Nabarro-pinned kinks at low activity to travelling kinks, stripes, and a bistable coexistence region as activity and on-site stiffness imposed by beam compression are varied. A continuum reduction to the non-linear Klein–Gordon equation with advection-like non-reciprocal coupling captures the phase diagram and yields analytic predictions for wave velocity that agree quantitatively with experiments and simulations. In the parameter space of activity and compression we also observe critical exceptional points both experimentally and in simulation. This work reveals how the interplay of non-reciprocity, non-linearity, and boundary conditions can be harnessed to program multistable dynamics in active metamaterials, opening pathways toward adaptive locomotion and robust functionality in complex environments.