Chiral Phonons Induced from Spin Dynamics via Magnetoelastic Anisotropy

We propose a mechanism to obtain chiral phononlike excitations from the bond-dependent magnetoelastic couplings in the absence of out-of-plane magnetization and magnetic fields. By mapping the hybrid excitation to its phononic analog, we reveal the impact of the lattice symmetry on the origin of the chirality. In the example of a triangular lattice ferromagnet, we recognize that the system is equivalent to the class D of topological phonons, and show the tunable chirality and topology by an in-plane magnetic field. As a possible experimental probe, we evaluate the phonon magnetization and planar thermal Hall conductivity. Our study gives a new perspective on tunable topological and chiral excitations beyond the Raman spin-lattice coupling, suggesting possible applications of spintronics and phononics in various anisotropic magnets and/or Kitaev materials.