Kinetomagnetism of chirality: giant chiral phonons in helical spins

Magnetism arises from the electron's spin and its orbital motion. Distinctly different from conventional magnetism, moving electrons in a chiral nonmagnetic material induce magnetization along the direction of the current. From the symmetry perspective, the motion of an object in a chiral crystal can induce magnetization. In recent pump-probe experiments, chiral phonons have been found to carry an exceedingly large moment. These chiral phenomena are proposed to align with the broader concept of 'kinetomagnetism of chirality,' which postulates that moving quasiparticles in chiral systems can induce magnetization along their direction of motion. Here, we present measurements of resonant inelastic X-ray scattering (RIXS) demonstrating that giant chiral phonons are induced by helical spins in Mn-doped Ni$_3$TeO$_6$, a chiral and polar multiferroic. The phonon excitations probed by RIXS with circularly polarized X-rays show pronounced circular dichroism in the helical-spin phase, resulting from the antisymmetric exchange interaction, i.e., the Dzyaloshinskii-Moriya interaction, between neighboring non-collinear spins. Our findings verify the hypothesis of kinetomagnetism of chirality, highlighting the connection between phonon motion and induced magnetization.