Exciton-Activated Phonon Magnetic Moment in Monolayer MoS₂

Optical excitation of chiral phonons plays a vital role in studying the phonon-driven magnetic phenomena in solids. Transition metal dichalcogenides host chiral phonons at high symmetry points of the Brillouin zone, providing an ideal platform to explore the interplay between chiral phonons and valley degree of freedom. In this talk, I will present helicity-resolved magneto-Raman studies of monolayer MoS₂, in which a doubly degenerate-point chiral phonon mode is found at ∼270cm⁻¹. Our wavelength- and temperature-dependent measurements show that this chiral phonon is activated through the resonant excitation of A exciton. Under an out-of-plane magnetic field, the chiral phonon exhibits giant Zeeman splitting, which corresponds to an effective magnetic moment of ∼2.5μ_B. I will conclude by discussing the ingredients that may be responsible for the coupling between exciton and chiral phonon. Our study provides important insights into lifting the chiral phonon degeneracy in an achiral nonmagnetic material, paving a route to excite and control chiral phonons.