Discovery of terahertz-frequency orbitally coupled magnons in a kagome ferromagnet

Mengqian Che; Weizhao Chen; Maoyuan Wang; F Michael Bartram; Liangyang Liu; Xuebin Dong; Jinjin Liu; Yidian Li; Hao Lin; Zhiwei Wang; Enke Liu; Yugui Yao; Zhe Yuan; Guang-Ming Zhang; Luyi Yang

doi:10.1126/sciadv.adw1182

Discovery of terahertz-frequency orbitally coupled magnons in a kagome ferromagnet

Sci Adv. 2025 Jul 4;11(27):eadw1182. doi: 10.1126/sciadv.adw1182. Epub 2025 Jul 4.

Authors

Mengqian Che¹, Weizhao Chen², Maoyuan Wang³, F Michael Bartram¹, Liangyang Liu¹, Xuebin Dong⁴, Jinjin Liu^{5

6}, Yidian Li¹, Hao Lin¹, Zhiwei Wang^{5

6}, Enke Liu⁴, Yugui Yao^{5

6}, Zhe Yuan^{7

8}, Guang-Ming Zhang^{1

9}, Luyi Yang^{1

9}

Affiliations

¹ State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.
² Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing 100875, China.
³ Department of Physics, Xiamen University, Xiamen 361005, China.
⁴ Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
⁵ Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing 100081, China.
⁶ Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, School of Physics, Beijing Institute of Technology, Beijing 100081, China.
⁷ Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200433, China.
⁸ Interdisciplinary Center for Theoretical Physics and Information Sciences (ICTPIS), Fudan University, Shanghai 200433, China.
⁹ Frontier Science Center for Quantum Information, Beijing 100084, China.

Abstract

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 terahertz at 6 kelvin, 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 an unconventional category of magnons in a ferromagnet stemming from orbital magnetic moments and position Co₃Sn₂S₂ as a promising candidate for high-speed terahertz spintronic applications.