Terahertz cavity magnon-polaritons in Gd0.5Ho0.5FeO3 single crystals tuned with temperature and magnetic field

The strong coupling between photons and magnons, enhanced by an electromagnetic cavity, has garnered significant attention, particularly in the frequency range of terahertz (THz). The hybrid nature of the coupled states provides an ideal platform for developing ever faster and less dissipative information processing. Hereby, we employed THz time-domain spectroscopy to study the vacuum cavity–magnon coupling phenomenon based on Gd0.5Ho0.5FeO3 single crystal. The high quality crystal itself acts as a Fabry–Pérot cavity, enabling strong coupling between cavity and magnon modes by carefully tuning magnon modes of the crystal. By altering the external magnetic field and temperature, the magnon frequencies can be tuned accordingly, and distinct anticrossing behaviors between the cavity and magnon modes have been demonstrated. The pronounced vacuum Rabi splitting, exceeding the linewidth of the polariton branches, further confirms the presence of strong light–matter interaction. These findings demonstrate that the coupling strength can be effectively controlled by dynamically tuning the magnetic field and temperature, thereby enabling the exploration of cavity–magnon interactions in the THz frequency. This study provides insights into the photon–magnon coupling mechanisms in rare-earth orthoferrites and lays the foundation for developing devices with advanced magneto-optical properties and cavity-based spintronic applications.