Tunable polarization magneto-optical effects at scattering of terahertz radiation on graphene nanoribbon gratings in a magnetic field

Background. The purpose of the work is a numerical study of the features of resonant (due to the excitation and propagation of plasmonic excitations) polarization magneto- optical (MO) effects and methods for controlling the polarization of THz radiation during scattering on graphene nanoribbon gratings in an external magnetic field. Materials and methods. Graphene is a 2D material with unique optical and electronic properties. It serves as a platform for new THz applications and microminiature systems with new capabilities. Excitation of surface magnetoplasmons-polaritons with a dispersion law changed due to the application of an external magnetic field significantly enhances MO effects in graphene structures. For the first time, a numerical study of polarization MO effects was carried out by automated modeling methods using the CST MWS software package based on the solution (using the finite element method in the frequency domain) of the electrodynamic problem of TEM wave diffraction on a graphene nanoribbon grating with the application of a perpendicular external magnetic field and analysis of the diffracted field characteristics in the THz range. Results. The results of modeling 3D e-Field scattering patterns of a normally incident p-polarized TEM wave on a cell of a graphene nanoribbon grating in a perpendicular external magnetic field at the frequencies of plasmon resonance (at B0 = 0) and magnetoplasmon resonances for different values of B0 (2, 4, 7, 10 T) were obtained. Based on the analysis of the results of calculating the ratio of the horizontal and vertical components Ex/Ey of the diffracted field and the axial ratio AR at the cross-section points (φ = 0°) of the main lobe of the 3D e-Field scattering patterns, the polarization type of the scattered THz radiation was studied and the Faraday rotation angle of the polarization plane of the transmitted wave and the Kerr rotation angle describing the rotation of the polarization axis of the reflected wave were calculated. Conclusions. It follows from the results of the numerical study that at the diffraction of a normally incident TEM-wave with p-polarization on a cell of the graphene nanoribbon grating with the application of a perpendicular external magnetic field at the frequencies of magnetoplasmon resonances frequency-tunable MO-effects are observed: 1) rotation of the polarization plane of a linearly polarized wave transmitting through a magnetized graphene grating, when the wave vector of the incident wave is parallel to the vector of the external magnetic field intensity (Faraday effect), while the Faraday rotation angle depends on the value of the external magnetic field; 2) changes in the orientation of polarization and ellipticity of the reflected wave (polar Kerr MO-effect), a linearly polarized THz wave, reflected from magnetized graphene, becomes elliptically polarized; in this case, the major axis of the polarization ellipse rotates by a certain angle with respect to the plane of polarization of the incident THz radiation proportional to the magnitude of the external magnetic field.