Chiral sound waves in strained Weyl semimetals

We show that a strained wire of a Weyl semimetal supports a new type of gapless excitation, the chiral sound wave (CSW). The CSW emerges due to the axial-axial-axial (AAA) triangle anomaly which couples the chiral charge density to elastic axial gauge fields. The CSW may propagate for long distances as it does not couple directly to quickly dissipating electromagnetic plasmons, and its damping is controlled by the slow chirality flip rate. The chiral phonons propagate along the strain-induced axial magnetic field, and not in the opposite direction. We propose an experimental setup to detect the chiral sound, which is excited by mechanical vibrations of the crystal lattice in the GHz frequency range. Our findings contribute to a new trend, the chiral acoustics, in strained Weyl semimetals.