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We demonstrate that an achiral active elastic ring, exhibiting spontaneous rotation, can generate reversible mechanical nonreciprocity despite having reciprocal passive interactions. This nonreciprocity arises from off-center elastic forces that reorient propulsion, creating a feedback loop between deformation and motion. Reversing the direction of rotation directly reverses the antisymmetric response, with critical amplification near a Hopf bifurcation leading to self-sustained traveling deformations.
Achiral active matter spontaneously generates reversible nonreciprocity by coupling deformation to rotation, bypassing the need for inherent chirality or external driving.
Nonreciprocal mechanical response is usually associated with built-in directional couplings, structural chirality, or external driving. Whether an achiral active body can instead generate and reverse such directionality through its own motion remains less clear. Here we show that spontaneous rotation makes an active elastic ring with reciprocal passive interactions mechanically nonreciprocal. Off-center elastic forces reorient propulsion, coupling deformation back to motion. Reversing the rotation reverses the antisymmetric response, while a compensating control preserves finite directionality but strongly suppresses the near-Hopf resonance. Approaching Hopf, the selected response grows inversely with distance to onset and becomes a self-sustained traveling deformation above threshold. Thus nonreciprocity is selected by the dynamical state, while active feedback controls its critical amplification.
