Chiral phonons in polar LiNbO₃

Collective lattice excitations called phonons and their symmetry classification are of fundamental importance for physical processes such as transport phenomena and phase transitions. Recent studies have introduced chirality as an additional degree of freedom in lattice vibrations, which is of special interest because chiral phonons carry angular momentum and therefore intrinsically break time-reversal symmetry. Here, we directly prove the presence of chiral phonons in a prototypical polar LiNbO₃ crystal. Our demonstration of chiral phonons in a ferroelectric enables in-situ electrical control of momentum-dependent “magnetic” polarization with reversible phonon handedness, i.e., dynamical multiferroicity. This ferroic control of phonon chirality has substantial potential in the emerging field of chiral phononics, particularly for controlling phonon angular momentum.