Axial-field-induced chiral channels in an acoustic Weyl system

Condensed-matter and other engineered systems, such as cold atoms ¹ , photonic ² or phononic metamaterials ³ , have proved to be versatile platforms for the observation of low-energy counterparts of elementary particles from relativistic field theories. These include the celebrated Majorana modes ⁴ , as well as Dirac ^5,6 and Weyl fermions ^7–9 . An intriguing feature of the Weyl equation ¹⁰ is the chiral symmetry, where the two chiral sectors have an independent gauge freedom. Although this freedom leads to a quantum anomaly ^11–15 , there is no corresponding axial background field coupling differently to opposite chiralities in quantum electrodynamics. Here, we provide the experimental characterization of the effect of such an axial field in an acoustic metamaterial. We implement the axial field through an inhomogeneous potential ¹⁶ and observe the induced chiral Landau levels. From the metamaterials perspective these chiral channels open the possibility for the observation of non-local Weyl orbits ¹⁷ and might enable unidirectional bulk transport in a time-reversal-invariant system ¹⁸ .