Ultrafast Spin-Phonon Coupling in van der Waals Antiferromagnets

Van der Waals (vdW) antiferromagnets present a unique platform for exploring spin-lattice coupling due to their anisotropic interactions within and between atomic layers. Tracking spin and lattice dynamics on ultrafast time scales can provide important insights into the fundamental processes of coupled degrees of freedom, including electron, spin, and lattice. Using ultrafast optical, x-ray scattering, and electron microscopy, we reveal how magnetic order couples with optical and acoustic phonons in real time. For example, below the Néel temperature of FePSe₃, the electron-phonon scattering rate on femtosecond time scales is reduced, indicating that the electronic energy is preferably coupled to the spin order before thermalizing with the lattice. At tens of picosecond time scales, both the magnitude and wavevector of the excited acoustic waves in FePS₃ can be significantly changed by the magnetic order, a phenomenon that has not yet been observed in 3D antiferromagnets. The discovery of strong spin-lattice coupling in vdW antimagnets opens opportunities for applications in ultrafast strain-tuning magnetism, magnetic sensors, and nanomechanical oscillators.

This work is primarily supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under award no. DE-SC-0012509.