Coherent Spin-Lattice Coupling in van der Waals Magnetic Crystals

The enormous potential of van der Waals (vdW) magnets in nanoscale information storage and spintronic technologies has stimulated a great deal of research into their equilibrium magnetic and structural properties. Nevertheless, comparatively little is known about their behavior under non-equilibrium conditions or the nature of magneto-structural coupling in this material class on its intrinsic ultrafast timescale. This talk will discuss our recent studies of non-equilibrium lattice and spin dynamics in vdW magnets using ultrafast spectroscopy. We will begin with CrI₃, where we observe strong light-driven coherent lattice oscillations, commensurate with phonon modes of A_1g symmetry. Intriguingly, the amplitude of the c-axis A_1g mode shows a strong pump helicity dependence below the magnetic ordering temperature. The correlation between magnetic order and vibrational amplitude of this mode is indicative of a strong coherent coupling between the spin and lattice degrees of freedom. Our ab initio and dynamic simulations suggest that this coupling originates from the modulation of exchange interactions through the distortion of the lattice. We will then discuss our recent results involving spin-phonon coupling in exfoliated flakes of Mn₃Si₂Te₆. Here, we observe a sudden temperature-dependent shift in the frequency of a coherent phonon mode, excited via impulsive stimulated Raman scattering, below the ferrimagnetic ordering temperature. This suggests that long-range spin order can significantly stiffen the crystal lattice through an analogous exchange-mediated mechanism. Our work highlights the strong interplay between the lattice and spin structure in layered magnetic materials, providing crucial insight for the realization of the next generation of high-speed nanoscale magneto-optic technologies.