Nonlocal Acoustic Moiré Hyperbolic Metasurfaces

• Published in: Advanced materials (Weinheim) Vol. 36; no. 18; pp. e2311350 - n/a
• Main Authors: Han, Chenglin, Fan, Shida, Li, Changyou, Chen, Li‐Qun, Yang, Tianzhi, Qiu, Cheng‐Wei
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.05.2024
• Subjects: Acoustic properties; Acoustic waves; Acoustics; Bilayers; dispersion engineering; Fields (mathematics); flat band; hyperbolic metasurfaces; Metasurfaces; Multilayers; Polaritons; Topology; twisted trilayer; twistronics; hyperbolic metasurfaces; dispersion engineering; twisted trilayer; flat band; twistronics
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202311350

The discovery of the topological transition in twisted bilayer (tBL) materials has attracted considerable attention in nano‐optics. In the analogue of acoustics, however, no such topological transition has been found due to the inherent nondirectional scalar property of acoustic pressure. In this work, by using a theory‐based nonlocal anisotropic design, the in‐plane acoustic pressure is transformed into a spatially distributed vector field using twisted multilayer metasurfaces. So‐called “acoustic magic angle”‐related acoustic phenomena occur, such as nonlocal polariton hybridization and the topological Lifshitz transition. The dispersion becomes flat at the acoustic magic angle, enabling polarized excitations to propagate in a single direction. Moreover, the acoustic topological transition (from hyperbolic to elliptic dispersion) is experimentally observed for the first time as the twist angle continuously changes. This unique characteristic facilitates low‐loss tunable polariton hybridization at the subwavelength scale. A twisted trilayer acoustic metasurface is also experimentally demonstrated, and more possibilities for manipulating acoustic waves are found. These discoveries not only enrich the concepts of moiré physics and topological acoustics but also provide a complete framework of theory and methodologies for explaining the phenomena that are observed. The topological transition in twisted bilayer materials has attracted considerable attention in nano‐optics. In the analogue of acoustics, however, no such topological transition has been found experimentally due to the inherent scalar property of sound pressure. In this work, by using a nonlocal design, the in‐plane acoustic pressure is transformed into a spatially distributed vector field using twisted multilayer metasurfaces.