Baydin, AndreyHayashida, KenjiMakihara, TakumaTay, FuyangMa, XiaoxuanRen, WeiMa, GuohongNoe, G. TimothyKatayama, IkufumiTakeda, JunNojiri, HiroyukiCao, ShixunBamba, MotoakiKono, Junichiro2023-04-252023-04-252023Baydin, Andrey, Hayashida, Kenji, Makihara, Takuma, et al.. "Magnetically tuned continuous transition from weak to strong coupling in terahertz magnon polaritons." <i>Physical Review Research,</i> 5, no. 1 (2023) American Physical Society: https://doi.org/10.1103/PhysRevResearch.5.L012039.https://hdl.handle.net/1911/114826Depending on the relative rates of coupling and dissipation, a light-matter coupled system is either in the weak- or strong-coupling regime. Here, we present a unique system where the coupling rate continuously increases with an externally applied magnetic field while the dissipation rate remains constant, allowing us to monitor a weak-to-strong coupling transition as a function of magnetic field. We observed a Rabi splitting of a terahertz magnon mode in yttrium orthoferrite above a threshold magnetic field of ∼14 T. Based on a microscopic theoretical model, we show that with increasing magnetic field the magnons transition into magnon polaritons through an exceptional point, which will open up new opportunities for in situ control of non-Hermitian systems.engPublished by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Journal articlePhysRevResearch-5-L012039https://doi.org/10.1103/PhysRevResearch.5.L012039