The coherent nonlinear dynamics between collective excitations, such as magnons and phonons, drive emergent phenomena in quantum materials, yet their direct observation remains a central challenge. Here, using double-terahertz-pump optical-probe spectroscopy, we report the direct observation of coherent magnon-phonon three-wave mixing in the layered antiferromagnetic insulator FePS3. We resolve both second- and third-order nonlinear responses of antiferromagnetic magnons and identify a suite of nonlinear couplings in two-dimensional (2D) coherent spectra, including definitive sum- and difference-frequency generation between magnons and phonons. These results lay the groundwork for exploiting coherent nonlinearities to entangle magnetic and vibrational excitations, opening avenues for quantum control and hybrid quantum technologies in the terahertz regime.
@article{arxiv.2605.20067,
title = {Coherent terahertz magnon-phonon three-wave mixing in a layered antiferromagnet},
author = {Liangyue Li and Na Wu and Zhengwang Lin and Zefen Li and Lixin Liu and Emil Vinas Boström and Yuan Wan and Xinbo Wang and Jianlin Luo and Fucai Liu and Angel Rubio and Qi Zhang},
journal= {arXiv preprint arXiv:2605.20067},
year = {2026}
}