Distinct Optical Excitation Mechanisms of a Coherent Magnon in a van der Waals Antiferromagnet

TL;DR

This study explores how different optical excitation mechanisms generate coherent magnons in a van der Waals antiferromagnet, revealing polarization-dependent effects and strategies for magnetic mode control using tailored laser pulses.

Contribution

It uncovers two distinct magnon excitation mechanisms in NiPS₃ by tuning photon energy and polarization, advancing understanding of ultrafast magnetic control.

Findings

Identification of polarization-dependent magnon excitation mechanisms

Change in excitation dependence when tuning photon energy

Potential for manipulating magnetic modes via sub-gap states

Abstract

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.