Zero-field magnon-photon coupling in antiferromagnet CrCl3

We experimentally and theoretically study the coupling between magnons and microwave photons at zero static magnetic field in a system combined by a planar superconducting cavity and a van der Waals antiferromagnetic insulator CrCl3 crystal. Using high-temperature superconductor DyBaCO, we fabricate a planar superconducting cavity with a high-quality factor. The antiferromagnetic resonance of CrCl3 has a finite resonance frequency within a microwave electronics range at zero static magnetic field, and this frequency is sensitive to the temperature. Tuning the temperature to make the antiferromagnetic resonance mode of CrCl3 approaching the cavity mode, we experimentally achieve the coupling between the magnon in CrCl3 and the microwave photon in cavity. An anticrossing feature of the transmission spectra mapping indicates the coupling of magnons and photons at zero static magnetic field. The cooperativity of the hybrid system is 76, indicating a strong coherent information exchange between photons and magnons in CrCl3.