Transmission property of one-dimensional Dirac-semimetal-defected photonic crystal in terahertz multi-bandgap

Abstract A symmetrical one-dimensional (1D) photonic crystal structure with a Dirac-emimetal-defected layer is proposed. The material properties of the Dirac semimetal are governed by three key parameters: Fermi level, Fermi velocity, and degeneracy factor. Simulation results demonstrate that the proposed structure generates multiple photonic bandgaps within the THz frequency range. In the low-THz region, pronounced resonant transmission peaks emerge, enabling near-perfect filtering performance. The positions of these defect modes can be dynamically tuned by adjusting the Fermi level and degeneracy factor. In mid- and high-THz frequency bands, the Dirac semimetal begins to exhibit metallic behavior, leading to attenuation of the transmission peaks and the appearance of absorption. The elevation of the Fermi level delays the critical threshold for the transition from the dielectric state to the metallic state, while an increase in Fermi velocity suppresses metallic behavior. Therefore, enhancing both the Fermi level and Fermi velocity contributes to strengthening the defect peak intensity. Conversely, increasing the degeneracy factor strengthens the metallic characteristics, thereby disrupting the high-frequency photonic bandgap. Notably, the defect layer thickness and incident angle exert significant influence on the transmission behavior: a larger incident angle causes the defect peak to shift toward higher frequencies and reduces its intensity, whereas a thicker defect layer shifts the defect peak toward lower frequencies. The modulation effects of both parameters become more pronounced as frequency increases. Compared with conventional photonic crystals, our work can provide a tunable structure over transmission properties, offering novel strategies for designing tunable filters and optical sensors.