Observation of kink control and generation via phonons in a system with no Peierls-Nabarro potential barrier

Localized transitions between distinct states, called kinks, with widths comparable to the discreteness of the system in which they reside, underpin important phenomena such as crystal plasticity and serve as carriers of topologically robust information. Phonon-kink interaction has been studied in systems such as the φ⁴ model, which presents a potential approach for kink control. However, discreteness has been a challenge in realizing phonon control of kinks due to the existence of Peierls-Nabarro barrier, which costs additional energy to overcome locally. In this work, we identify this barrier free system—a one-dimensional (1D) topological mechanical metamaterial supporting a nonlinear zero mode (kink)—to overcome this challenge and report the first experimental observation of kink control and generation via small amplitude vibrational wavepackets (i.e., phonons) in a system with zero Peierls-Nabarro barrier, regardless of discreteness. Creating an elastically-coupled realization of the Kane-Lubensky chain (a type of topological metamaterial that supports localized modes with zero energy cost for quasi-static deformation), we find excellent agreement between experiments and computational predictions. We also numerically observe a continuous family of kink solutions as a function of the kink center and phonon-kink dynamics that are different from other nonlinear discrete systems. In particular, we simulate long-duration kink motion, which has important implications for kink control. Considering the nonlinear zero modes supported by our system, these findings enable remote control of extreme material stiffness, e.g., soft on one side and stiff on the other, vice versa, or stiff on both. Further future potential applications include locomotion, shape-shifting materials, and signal processing and transmission.