Coupling Between Microwave Cavity And Magnon In Antiferromagnet CrCl₃

Cavity magnonics composed of cavity quantum electrodynamics and magnetism is an emerging interdiscipline that focuses on the interaction between magnon and photon.Photons and spins with high mobility and long coherence time can used to transmit quantum information between different quantum components.The hybrid displays both spin and photon properties can be generated when the coupling of magnon and photon occurs,and the hybrid expects to have a wide application prospect in quantum information processing and spintronics.Focus on ferromagnetic materials with high spin density,remarkable progress has been made,such as coherent coupling and dissipative coupling,realizing the strong coupling in ferromagnetic metal with nanometer thickness,and exploring special coupling points.Antiferromagnetic materials are expected to be used in the design and fabrication of stable high-speed memory devices because of their faster spin dynamics and better stability than ferromagnet.Few studies on the coupling between antiferromagnetic magnon and photon,such as DyFeO3,Fe2Mo3O8,and α-Fe2O3.There are some difficulties of antiferrmagnet-cavity coupling,（1）The detection of antiferromagnetic resonance requires the terahertz technology and the large static magnetic field.（2）The coupling between antiferromagnetism and resonator is only discussed when the magnetic moments are antiparallel.（3）It is difficult to construct a high frequency resonator with good performance.Therefore,it’s important to study antiferromagnet-cavity coupling at lower frequencies.Focus on the two-dimension antiferromagnet CrCl₃ crystal and high temperature superconducting strip cavity,we studied the antiferromagnetic resonance with spin-flop transition,antiferromagnet and cavity coupling,zero-field magnon-photon coupling,and magnon-magnon coupling.We clarified the spin dynamic of CrCl₃ and the coupling mechanism between antiferromagnet and cavity,and we proposed a new method for realizing zero-magnetic field magnon-photon coupling and magnon-magnon long-distance coupling.Our research provides the physical basis and device prototype for the development of emerging spintronics devices and the construction of quantum hybrid systems.The research content includes the following parts:（1）We study the spin dynamic of antiferromagnetic CrCl₃ crystal,and analyse the antiferromagnetic resonance in spin-flop transition.We confirm that the optical mode and acoustic mode can be separately excited by changing the symmetry of the external magnetic field and the microwave magnetic field.（2）We studied the antiferromagnetic resonance optical and acoustic modes coupling with cavity modes and clarified the coupling mechanism of antiferromagnetic resonance and cavity.By changing the position of the CrCl₃ crystal on the cavity,we separately demonstrate the cavity modes coupled with the acoustic and optical modes of antiferromagnetic resonance when the magnetic moments are noncolinear.We predict that both the net magnetization and the Neel 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.（3）We realize the magnon-photon coupling at zero magnetic field.Without the magnetic field applied,we adjust the antiferromagnetic resonance mode close to the cavity mode by changing the temperature and observe the anticrossing characteristics of coupling modes which demonstrate the magnon-photon coupling.By analyzing the dissipation and coupling strength of the magnetron and resonator,the coordination of the hybrid system is 76,which indicates the strong coherent information exchange between the magnetron and resonator.（4）We demonstrated that the magnon and magnon coupling using the microstrip transmission line.The indirect coupling between the optical and acoustic modes in CrCl₃ crystal is realized by adjusting the direction of the static magnetic field to break the symmetry and antisymmetry with the microwave magnetic field.The in-phase and out-of-phase precession of the magnons of acoustic and optical modes will cause the constructive or destructive interference of the coupled modes.To achieve the distance coupling of the optical and acoustic modes,we apply magnetic fields in different directions on two CrCl₃ crystals located several centimeters apart on the microstrip line.The level repulsion and attraction of optical and acoustic modes can be adjusted by changing the spacing of two samples to adjust their phase difference.