van der Waals metamaterials
William Dorrell, Harris Pirie, S. Minhal Gardezi, Nathan C. Drucker, Jennifer E. Hoffman
Abstract
The van der Waals heterostructures are an active frontier for discovering emergent phenomena in condensed matter systems. They are constructed by stacking elements of a large library of two-dimensional materials that couple together through van der Waals interactions. However, the number of possible combinations within this library is staggering, so fully exploring their potential is a daunting task. Here, we introduce van der Waals metamaterials to rapidly prototype and screen their quantum counterparts. These layered metamaterials are designed to reshape the flow of ultrasound to mimic electron motion. In particular, we show how to construct analogs of all stacking configurations of bilayer and trilayer graphene through the use of interlayer membranes that emulate van der Waals interactions. By changing the membrane's density and thickness, we can also reach coupling regimes far beyond that of naturally occurring graphene. We anticipate that van der Waals metamaterials can be used to explore, extend, and inform future electronic devices. Furthermore, they allow the transfer of useful electronic behavior to acoustic systems, such as flat bands in magic-angle twisted bilayer graphene, which may aid the development of superresolution ultrasound imagers.