Experimental Demonstration of Dual‐Band Nano‐Electromechanical Valley‐Hall Topological Metamaterials

Abstract Suppression of undesired backscattering of very‐high‐frequency elastic signals has been considered as a grand challenge in integrated phononic circuits. Originating from condensed‐matter physics, valley‐Hall topological insulators provide an intriguing strategy to overcome this challenge. To date, phononic valley‐Hall topological insulators have been demonstrated only in bulk acoustic and mechanical systems operating at relatively low frequencies. Here, an integrated nano‐electromechanical valley‐Hall topological insulator operating in the very‐high‐frequency regime is experimentally realized. Valley kink states that are backscattering‐immune against sharp bends and exhibit the “valley‐momentum locking” effect simultaneously in the fundamental (≈60 MHz) and second‐order (≈120 MHz) frequency bands are demonstrated. It is further shown that the propagation directions of these dual‐band valley kink states are always locked to their valley pseudospins. The results not only enable various applications in very‐high‐frequency integrated phononic circuits with enhanced robustness and capacity, but also open the door to experimental exploration of mechanical nonlinearities, particularly those involving the fundamental and second‐order frequencies, in topologically nontrivial nanostructures.