Strong Strain-Induced Coupling between Nanomechanical Pillar Resonators

Networks of coupled resonators are an ubiquitous concept in physics, forming the basis of synchronization phenomena, metamaterial formation, nonreciprocal behavior and topological effects. Such systems are typically explored using optical or microwave resonators. In recent years, mechanical resonators have entered the stage as universal building block for resonator networks, both for their well-controlled mechanical properties and for their eigenfrequencies conveniently located in the radio-frequency regime. Vertically oriented nanomechanical pillar resonators are ideally suited for the dense integration into large resonator networks. However, to realize the potential of these promising systems, an intrinsic coupling mechanism needs to be established. Here, we demonstrate strain-induced, strong coupling between two adjacent nanomechanical pillar resonators. The coupling is mediated through the strain distribution in the joint substrate caused by the flexural vibration of the pillars, such that the coupling strength can be controlled by the geometric properties of the nanopillars as well as their separation. Both, mode hybridization and the formation of an avoided level crossing in the response of the nanopillar pair are experimentally observed. The coupling mechanism is readily scalable to large arrays of nanopillars, enabling all-mechanical resonator networks for the investigation of a broad range of collective dynamical phenomena.