Research Of Electromagnetically Induced Transparency Based On Dirac Semimetal Metamaterials

Terahertz waves generally refer to electromagnetic radiation in the frequency range of 0.1 to 10 THz,which is situated between millimeter wave and infrared.Because of the particularity of the position of THz wave in the electromagnetic spectrum,it has a very broad application prospect in aspects of safety monitoring,medical imaging,sensing detection and communication technology.However,the THz technology is constrained in many applications due to the existence of enormous material losses and the difficulties in controlling permittivity functions.Three-dimensional(3D)Dirac semimetal(hereinafter referred to as Dirac semimetal),also known as 3D graphene,but,compared to graphene,3D Dirac semimetals are more robust against environmental defects or excess conductive bulk states and easier to process and have stable performance.Thus,it has unique advantages in the development of THz functional devices.In this paper,the 3D Dirac semimetal based electromagnetically induced transparency(EIT)will be studied.1.By using bright-bright model coupling method and constructing two-parallel-strip structure,the EIT-like optical response can be induced.The research shows that both the upper and lower strips can be simultaneously excited by the incident light and two resonance modes and diplo modes can be observed both in spectrum and electric field distribution diagram,respectively;when the two strips with different length are placed together,the plasmon-induced transparency(PIT)effect can be observed due to the week hybridization between the two modes.In the spectrum,a transmission peak,called transparency window,appears in the middle of the two original resonance dips,and in the electric field diagram,a quadrupole modes.We discussed the effect of some important structural parameters(e.g.lateral displacement s,the length of upper strip)on the PIT spectrum.Utilizing the conductivity tunability of the Dirac semimetal,we demonstrate the frequency shift characteristic with different Fermi energy;meanwhile thanks to the tunability of the PIT window,we get the group delays under different PIT spectra and group delays of more than 1.86ps are obtained under different Fermi energy in our simulations.2.By using bright-dark model coupling method and constructing cross-shaped structure,the EIT-like optical response can be induced.By investigating the transmission under different lateral displacement s,we find that the transparency window was induced due to the broken symmetry of the metamaterial structure.By investigating the electric field distribution in z-component,we find that the intrinsic mechanism of the appearance of the transparent window is due to the shift of the electric field,that is,from the bright mode to the dark mode.We also find that the PIT window can be broadened within a certain range by adjusting the structural parameter s.Similarly,we demonstrate the spectral tunability by changing the Fermi energy of Dirac semimetal.In this section,we also study the dependence of refractive index on frequency to demonstrate the practical application of PIT metamaterial in sensing.Meanwhile,a higher figure of merit(FoM)value of about 10.55 is obtained in our simulation.3.A tunable multiple plasmon-induced transparencies based on Dirac semimetal is studies in this section.Multiple transmission windows are obtained by adjusting the structural parameters;by analyzing the distribution of the electric field,we verify that two transparent were windows generated in the spectrum.We also investigated the transmission spectra with different Fermi energy and both the two transparency windows have a blue shift with Fermi energy increases.Similarly,we numerically calculated the group delays with different Fermi energy under the multi-transparency windows,and then,multi-frequencies slow-light effect was obtained.