Moire-Driven Topological Transitions and Extreme Anisotropy in Elastic Metasurfaces

The twist angle between a pair of stacked 2D materials has been recently shown to control remarkable phenomena, including the emergence of flat-band superconductivity in twisted graphene bilayers, of higher-order topological phases in twisted moire superlattices, and of topological polaritons in twisted hyperbolic metasurfaces. These discoveries, at the foundations of the emergent field of twistronics, have so far been mostly limited to explorations in atomically thin condensed matter and photonic systems, with limitations on the degree of control over geometry and twist angle, and inherent challenges in the fabrication of carefully engineered stacked multilayers. Here, this work extends twistronics to widely reconfigurable macroscopic elastic metasurfaces consisting of LEGO pillar resonators. This work demonstrates highly tailored anisotropy over a single-layer metasurface driven by variations in the twist angle between a pair of interleaved spatially modulated pillar lattices. The resulting quasi-periodic moire patterns support topological transitions in the isofrequency contours, leading to strong tunability of highly directional waves. The findings illustrate how the rich phenomena enabled by twistronics and moire physics can be translated over a single-layer metasurface platform, introducing a practical route toward the observation of extreme phenomena in a variety of wave systems, potentially applicable to both quantum and classical settings without multilayered fabrication requirements.

Automated summary

The twist angle between stacked 2D materials has been shown to control various phenomena, such as superconductivity and topological phases. However, these discoveries have been limited to atomically thin systems and photonic systems. This work demonstrates the application of twistronics in a macroscopic elastic metasurface made of LEGO pillar resonators, allowing for highly tailored anisotropy and strong tunability of waves. The findings show the potential for observing extreme phenomena in a variety of wave systems without the need for multilayered fabrication.