Coupling of microwave photons to optical and acoustic magnon modes in the layered antiferromagnetic insulator CrCl3

Abstract

We study a magnon-photon coupling system consisting of a layered antiferromagnetic insulator ${\mathrm{CrCl}}_{3}$ and a planar superconducting cavity. By changing the position of the ${\mathrm{CrCl}}_{3}$ crystal on the cavity, we separately demonstrate the cavity mode coupled with an acoustic mode and an optical mode when the magnetic moments are in a spin-flop transition. Based on the coupled Landau-Lifshitz-Gilbert equations and Kirchhoff's equation, we predict that both the net magnetization and the N\'eel vector contribute to the coupling between the optical mode and cavity mode, and only the net magnetization participates in the coupling of the acoustic mode and cavity mode. This paper highlights the vital role played by the N\'eel vector as the key parameter of an antiferromagnet in magnon-photon coupling, which offers insight into designing antiferromagnet spintronic devices.