In ferromagnetic materials, magnons - quanta of spin waves - typically resonate in the gigahertz range. Beyond conventional magnons, while theoretical studies have predicted magnons associated with orbital magnetic moments, their direct observation has remained challenging. Here, we present the discovery of two distinct terahertz orbitally-coupled magnon resonances in the topological kagome ferromagnet Co3Sn2S2. Using time-resolved Kerr rotation spectroscopy, we pinpoint two magnon resonances at 0.61 and 0.49 THz at 6 K, surpassing all previously reported magnon resonances in ferromagnets due to strong magnetocrystalline anisotropy. These dual modes originate from the strong coupling of localized spin and orbital magnetic moments. These findings unveil a novel category of magnons stemming from orbital magnetic moments, and position Co3Sn2S2 as a promising candidate for high-speed terahertz spintronic applications
@article{arxiv.2408.09417,
title = {Discovery of terahertz-frequency orbitally-coupled magnons in a kagome ferromagnet},
author = {Mengqian Che and Weizhao Chen and Maoyuan Wang and F. Michael Bartram and Liangyang Liu and Xuebin Dong and Jinjin Liu and Yidian Li and Hao Lin and Zhiwei Wang and Enke Liu and Yugui Yao and Zhe Yuan and Guang-Ming Zhang and Luyi Yang},
journal= {arXiv preprint arXiv:2408.09417},
year = {2025}
}