Van der Waals Metamaterials*

Van der Waals (vdW) heterostructures are a fertile frontier for discovering emergent condensed matter phenomena. They are constructed by stacking elements of a large library of two-dimensional materials, which couple together through vdW interactions. However, fully exploring the vast number of possible combinations within this library is a daunting task. Here we introduce vdW metamaterials to rapidly prototype and screen their quantum counterparts. These layered metamaterials reshape the flow of ultrasound to mimic electron motion. We first present a method to recreate the vdW interaction between layered phononic metamaterials using interlayer coupling membranes, which we can tune to create acoustic analogs of well-known vdW heterostructures, including all configurations of bilayer and trilayer graphene. We then twist coupled metamaterial layers to induce interesting phononic behavior mimicking twisted bilayer graphene. We anticipate vdW metamaterials will inform future electronic devices. Equally, they allow the transfer of useful electronic behavior to acoustic systems, such as flat bands in magic-angle twisted bilayer graphene, which may advance super-resolution ultrasound imaging.