Ultrafast coherent THz lattice dynamics coupled to spins in the van der Waals antiferromagnet FePS 3 .

Coherent THz optical lattice and hybridized phonon-magnon modes are triggered by femtosecond laser pulses in the antiferromagnetic van der Waals semiconductor FePS 3 . We investigate the laser-driven lattice and spin dynamics in a bulk crystal as well as in a 380 nm-thick exfoliated flake as a function of the excitation photon energy, sample temperature and applied magnetic field. The pump-probe magneto-optical measurements reveal that the amplitude of a coherent phonon mode oscillating at 3.2THz decreases as the sample is heated up to the Néel temperature. This signal eventually vanishes as the phase transition to the paramagnetic phase occurs, thus revealing its connection to the long-range magnetic order. In the presence of an external magnetic field, the optically triggered 3.2 THz phonon hybridizes with a magnon mode, which we utilize to excite the hybridized phonon-magnon mode optically. These findings open a pathway towards the optical control of coherent THz photo-magnonic dynamics in a van der Waals antiferromagnet, which can be scaled down to the two-dimensional limit. This article is protected by copyright. All rights reserved.