Análise de ressonâncias eletromagnéticas em estrutura periódica de discos de grafeno magnetizadosd na faixa de terahertz

Abstract

Since its isolation in 2004, graphene has shown to be a promising material, as it allows strong interaction of charge carriers with terahertz (THz) radiation. This extensive interaction with light is due to the excitation of surface plasmon polaritons (SPPs) thus providing several applications in the areas of THz photonics. In the presence of an external magnetic field, the cyclotron resonance dominates in the THz spectra. In this work we analyze several resonance modes (dipole, quadrupole, hexapole and modes with azimuthal symmetry) that can exist in the graphene disk in an arrangement with periodic square unit cells. We calculated the resonances with magnetization by an external DC magnetic field ranging up to 3T and compared them with the case of the same structure without magnetization where it was observed that the presence of the magnetic field results in the splitting of some resonant modes. The resonant characteristics are numerically obtained using the COMSOL Multiphysics software in two distinct and complementary studies: the eigenfrequency calculation regime referring to the natural modes of resonance and the plane wave excitation with normal incidence. Floquet boundary conditions on the four sides of the unit cells are used to simulate the in-plane periodic structure of graphene. The unit cell side (i.e. the period of the matrix) used in the numerical calculation is A = 9µm, the radius of the graphene disk is D = 3µm. The problem of excitation of some modes is discussed from the point of view of the circular symmetry that, to generate the resonance peaks in this regime, had to be broken through a subtle cut in the shape of a rectangular slit of size Lx = 10nm by Ly = 550nm starting axially from the edge. The disk is modeled as a two-dimensional element, and this provides a good approximation of the atomic thickness of a single layer of this material. Conductivity is modeled by the semi-classical Drude model. The discussion of resonator properties is fulfilled in terms of graphene currents and electromagnetic fields outside graphene. Potential applications of the obtained results are Faraday and Kerr rotators, controllable filters and absorbers for THz photonic circuits