Pseudo-magnetic fields for sound: Landau quantization and valley devices

Synthetic gauge fields offer a powerful way to manipulate the transport properties of Dirac quasiparticles. However, realizing customizable fields and sharp topological domain walls in electronic systems remains challenging. Surprisingly, these gauge fields affect sound waves in the same way as electron waves, allowing acoustic metamaterials to serve as a versatile and accessible platform to explore gauge-field physics. Here we experimentally realize a spatially uniform pseudo-magnetic field for airborne sound using a triaxially strained honeycomb lattice of coupled acoustic cavities. We observe discrete acoustic pseudo-Landau levels near the Dirac point, with strong sublattice polarization at the zeroth level and quantum-Hall-like edge states in the adjoining gap. Using a novel design that implements strain without deforming the honeycomb arrangement of cavities, we can combine metamaterial domains with different strain patterns to create a +B/-B junction. Our design could be used to create an acoustic valley polarizer which hosts valley-locked snake states at the junction.