Twisted van der Waals Metamaterials*

Twisted van der Waals (vdW) heterostructures have recently emerged as a tunable platform for studying correlated electrons. However, these materials require significant effort for theoretical and experimental exploration. Here we present a simple platform to reproduce twistronic behavior using acoustic metamaterials made of interconnected air cavities in stacked steel plates [1]. Our classical analog of twisted bilayer graphene (TBG) perfectly replicates the band structures of its quantum counterpart, including mode localization at a magic angle of 1.12°. We then tune the interlayer membrane thickness to achieve an acoustic magic angle as high as 6.01°, equivalent to applying 130 GPa to TBG. In this regime, the localized modes are over five times closer together than at 1.12°, increasing the strength of any emergent non-linear acoustic couplings. Our results enable greater inter-connectivity between quantum materials and acoustic research: twisted vdW metamaterials provide simplified models for exploring twisted electronic systems and may allow the enhancement of non-linear effects to be translated into acoustics.

[1] Gardezi, arxiv:2020.10037