Magnetically and Electrically Tunable Magnetooptical Absorption of Circularly Polarized Waves by a Graphene Metasurface in the Terahertz and Far-Infrared Ranges

Abstract

Background. The relevance of this topic is dictated by the needs of modern terahertz (THz) technology in the development of materials and techniques enabling the fabrication of efficient and widely tunable THz devices. The aim of this work is to simulate and numerically investigate the interaction of circularly polarized electromagnetic waves with a graphene metasurface and the behavior of magnetooptical (MO) absorption of right- and left-polarized THz radiation under the influence of external magnetic and electric fields in various combinations in the THz and far-IR ranges. Materials and methods. Metasurfaces based on nanostructured graphene in an external magnetic field have become the materials capable of expanding the scope of magnetoplasmonics to the THz and IR ranges. This is due to the strong MO response upon the excitation of surface magnetoplasmon polaritons. A numerical study of the interaction of circularly polarized THz waves with a graphene metasurface in an external magnetic field has been performed using automated modeling methods by using the CST Microwave Studio software package. The boundary value problem of electrodynamics is solved in the CST MWS program using the numerical finite element method (FEM) in the frequency domain. Results. The results of modeling the transmission, reflection, and MO absorption spectra of right- and left-polarized waves at normal and oblique incidence on a graphene metasurface in an external magnetic field B₀ are obtained as functions of B₀ (0, 2, 4, 7, and 10 T) for different incidence angles in the THz and far-IR ranges. The results of a numerical study of electrically and magnetically tunable MO absorption spectra of circularly polarized waves are presented as functions of the Fermi energy E_F (0.2, 0.7, and 1 eV) of graphene for different combinations of applied magnetic and electric fields in the THz and far-IR frequency ranges. Conclusions. The modeling results show that (i) With increasing B₀, the resonant nature of the MO absorption at the magnetoplasmon resonance frequencies of the right-polarized wave becomes more pronounced, while for the left-polarized wave, the resonant features become less pronounced. (ii) The controllability of the MO absorption of the graphene metasurface by the external magnetic field upon a variation the graphene Fermi energy E_F (by the external electric field) is optimal at E_F = –0.2 eV. With increasing B₀ at E_F =–0.2 eV, the frequencies f_res of the magnetoplasmon resonances and the maxima P_RCPmax of the absorption coefficient of the right-polarized wave increase, while for the left-polarized wave, the values of P_LCPmax decrease. (iii) With increasing incidence angle, the values of the MO absorption maxima P_RCPmax and P_LCPmax increase compared to those at normal (α = 0°) incidence; the difference in the MO absorption of the right- and left-polarized wave increases and is significant for α = 40° at E_F = –0.2 eV, especially at high values of B₀ = 10 T.