Distinct Optical Excitation Mechanisms of a Coherent Magnon in a van der Waals Antiferromagnet
arxiv(2024)
摘要
The control of antiferromagnets with ultrashort optical pulses has emerged as
a prominent field of research. Tailored laser excitation can launch coherent
spin waves at terahertz frequencies, yet a comprehensive description of their
generation mechanisms is still lacking despite extensive efforts. Using
terahertz emission spectroscopy, we investigate the generation of a coherent
magnon mode in the van der Waals antiferromagnet NiPS_3 under a range of
photoexcitation conditions. By tuning the pump photon energy from transparency
to resonant with a d-d transition, we reveal a striking change in the
coherent magnon's dependence on the pump polarization, indicating two distinct
excitation mechanisms. Our findings provide a strategy for the manipulation of
magnetic modes via photoexcitation around sub-gap electronic states.
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