Research On Electromagnetically Induced Transparency Of Dirac Semimetal Terahertz Metamaterials

Metamaterials is a new type of artificial electromagnetic material,which consists of periodic or non-periodic combination of unit structures with dimensions much smaller than wavelength.Through the interaction of basic unit structure and electromagnetic waves,the new artificial material provides a new design method for engineering design and scientific research,so that it has physical properties that natural materials or synthetic materials do not have.In the last few years,with the rapid development of terahertz wave technology,terahertz metamaterials have attracted widespread attention in the fields of biological sensing,slow light storage,phase modulation,and have injected new impetus into the development of terahertz functional devices.Electromagnetic induced transparency(EIT)originates from the interaction between light and matter,and its unique mechanism and non-linear characteristics have high research and application prospects.At the same time,with the emergence of a new type of Dirac semimetal semiconductor material,which is regarded as "3D graphene",compared with metal materials whose dielectric constant is difficult control and graphene which is susceptible to dielectric interference,Dirac semimetal has superior photoelectric performance and ultra-high carrier mobility,which further promotes the development of terahertz metamaterials.In this article,the terahertz metamaterial based on Dirac semimetal is proposed.Through the combination of theoretical analysis and modeling and simulation,the electromagnetic induction and transparency of terahertz metamaterials will be studied,and applied to functional devices such as modulators,sensors,and slow light.The main contents and summary are as follows:(1)By the detailed research and analysis of independent SRR and symmetric SRR structures,the metamaterials based on different SRR structures are designed to realize and reveal the typical induced transparency.The results show that the resonant frequency of the transmission spectrum can be flexibly adjusted by changing the refractive index of the metamatrial dielectric layer,and the performance of refractive index sensors is analyzed.Finally,we calculate the effects of different incident electromagnetic waves and Fermi energy on the transmission window.These features provide a new approach to the design of new terahertz functional metamaterials.(2)As combination of EIT and surface plasmon,plasmon-induced transparency has the advantage of EIT,can overcome the diffraction limit,and has a higher local field enhancement effect.The ultra-wideband tunable(PIT)effect based on Dirac semimetal is realized by the mode-dark mode magnetic coupling method.The magnetic field distribution and surface current in z direction with different frequencies are analyzed and studied.The physical mechanism of PIT effect is explained by using the three-level system in the atomic system.The bandwidth of PIT effect transmission spectrum can be flexibly adjusted by adjusting the size of metamaterials,thus realizing the ultra-wideband PIT effect.The effects of temperature,base refraction coefficient and Dirac semimetal Fermi level on the transmission spectrum are also analyzed.The simulation results show that the resonance frequency of PIT effect can be tuned by different Fermi energy of Dirac semimetal,and the new method for the adjustment of slow light effect can be provided.(3)A metamaterials structure based on complementary Dirac semimetal is designed,The basic unit includes strip structures and split ring resonator(SRR).The ultra-high Q(~87.6)of electromagnetically induced reflection is realized by the coupling of light mode and dark mode.The research shows that the corresponding reflection spectrum and electric field distribution of different offsets s of SRR can be calculated to further clarify the switching amplitude modulation of the reflection peak.Since plasmons of the terahertz wave are sensitive to the refraction coefficient of the nearby dielectric,we analyze the influence of refractive coefficients of different substrates on the reflectance spectrum.The numerical simulation results show that the designed electromagnetic induced reflection metamaterial structure can be used for refractive index sensing.Its sensitivity is 302.5GHz/RIU,and the figure of merit(FoM)reaches 19.(4)A novel Fano resonance system based on the symmetrical structure of Dirac semimetal metamaterials is designed and studied.The structure consists of the strip structure and symmetrical U-shaped SRRs.The novel Fano resonance is realized by destructive interference between the bright and dark modes.By analyzing the surface current distribution in z direction at the resonance frequency of transmission spectrum,the physical mechanism of Fano resonance is described in detail.The effects of different incident angles of electromagnetic waves and Fermi levels on resonant frequencies are discussed.Different from previous studies,we not only analyzed the influence of coating layers with different refractive coefficients on the transmission spectrum,but also analyzed the influence of different substrate materials on the sensitivity of the refractive index sensor.The simulation results show that the substrate material with low refractive coefficient is more beneficial to improve the sensitivity of the sensor.Most importantly,we can get higher group delay near the peak of transmission window.These characteristics provide guidance for the manufacture of biosensors and slow light devices in the terahertz field.