  Condensed-matter and other engineered systems, such as cold atoms, photonic,
or phononic metamaterials, have proven to be versatile platforms for the
observation of low-energy counterparts of elementary particles from
relativistic field theories. These include the celebrated Majorana modes, as
well as Dirac and Weyl fermions. An intriguing feature of the Weyl equation is
the chiral symmetry, where the two chiral sectors have an independent gauge
freedom. While this freedom leads to a quantum anomaly, 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
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 and might enable unidirectional bulk transport in a
time-reversal invariant system.
