Nonlocal Acoustic Moiré Hyperbolic Metasurfaces

Area of Science:

• Acoustics
• Condensed Matter Physics
• Materials Science

Background:

• Topological transitions are well-known in nano-optics but have not been observed in acoustics.
• Acoustic pressure's scalar nature limits topological phenomena, unlike optical vector fields.

Purpose of the Study:

• To explore topological transitions in acoustics using twisted multilayer metasurfaces.
• To induce and observe acoustic topological phenomena analogous to those in optical systems.
• To demonstrate a theoretical framework for manipulating acoustic waves.

Main Methods:

• Utilized a theory-based nonlocal anisotropic design for acoustic metasurfaces.
• Employed twisted multilayer metasurfaces to transform scalar acoustic pressure into a vector field.
• Experimentally observed acoustic topological transitions and polariton hybridization.

Main Results:

• Demonstrated "acoustic magic angle" phenomena, including nonlocal polariton hybridization and topological Lifshitz transitions.
• Observed acoustic topological transitions from hyperbolic to elliptic dispersion with changing twist angles.
• Achieved flat band dispersion at the acoustic magic angle, enabling unidirectional propagation of polarized acoustic excitations.

Conclusions:

• The study establishes a method for achieving topological transitions in acoustics, enriching moiré physics and topological acoustics.
• The findings provide a theoretical and experimental framework for manipulating acoustic waves at the subwavelength scale.
• Low-loss tunable polariton hybridization is facilitated by the observed phenomena.