Coherent helicity-dependent spin-phonon oscillations in the ferromagnetic van der Waals crystal CrI3

Abstract

The discovery of two-dimensional systems hosting intrinsic magnetic order represents a seminal addition to the rich landscape of van der Waals materials. CrI₃ is an archetypal example, where the interdependence of structure and magnetism, along with strong light-matter interactions, provides a new platform to explore the optical control of magnetic and vibrational degrees of freedom at the nanoscale. However, the nature of magneto-structural coupling on its intrinsic ultrafast timescale remains a crucial open question. Here, we probe magnetic and vibrational dynamics in bulk CrI₃ using ultrafast optical spectroscopy, revealing spin-flip scattering-driven demagnetization and strong transient exchange-mediated interactions between lattice vibrations and spin oscillations. The latter yields a coherent spin-coupled phonon mode that is highly sensitive to the driving pulse’s helicity in the magnetically ordered phase. Our results elucidate the nature of ultrafast spin-lattice coupling in CrI₃ and highlight its potential for applications requiring high-speed control of magnetism at the nanoscale.

CrI3 is a van der Waals material which exhibits magnetic ordering down to the monolayer limit. Here, using ultrafast optical spectroscopy, Padmanabhan and Buessen et al. investigate the coupling between the magnetically ordered spins and lattice distortions, finding a coherent spin-coupled phonon mode.