Ghost surface magnon-plasmon polariton in antiferromagnets covered with graphene monolayer.

We predicted one ghost surface magnon-plasmon polariton (GSMPP) in antiferromagnets covered a graphene monolayer in the out-plane geometry where both an external magnetic field and the antiferromagnetic easy axis are normal to the surface. This GSMPP exists in the frequency range that linearly increases with the external magnetic field. Due to the coupling between the external magnetic-field and electrons in the graphene monolayer, we found some interesting features of the GSMPP. (1) The frequency range of the GSMPP occupies the whole interval between the two antiferromagnetic resonant frequencies and linearly increases with the external magnetic field. (2) There two necessary conditions for the existence of GSMPP, or one is the existence of external magnetic field and the other is that the GSMPP frequency must be larger than the electronic-cyclotron frequency in the graphene monolayer so that the GSMPP exists in an enclosed triangular region in the frequency-field space. (3) The oscillatory behavior of GSMPP field and Poynting vector along the surface normal are very easily seen. (4) The surface conductivity of graphene monolayer and the antiferromagnetic permeability are controlled by the Femi-energy of graphene and external magnetic field, so the GSMPP is a highly-tunable surface polariton. The numerically-simulated attenuated total reflection (ATR) spectra prove that the GSMPP is a real-world existence and more easily observed in experiment. The results are interesting in spintronics and surface optics, as well as the relevant technology fields.