Chiral phonon-induced spin polarization

Controlling spins on very short time scales e may enable novel non-equilibrium magnetic physics as well as ultrafast spintronics for energy-efficient information processing. Strongly driven phonons directly influence the interatomic distances, orbital symmetry, and exchange interactions that are closely related to magnetism in materials. We excited chiral phonons using circular-polarized terahertz pulses and observed a prominent transient magneto-optic Kerr effect in rare-earth trihalides. The temperature dependence of the spin dynamics indicates a strong magnetic field generated by the phonons. Our result may open a new route to investigate spin-phonon interaction in ultrafast magnetism directly.