3D Dirac Semimetal Metamaterial Supported Terahertz Tunable Dual-Functional Polarization Converter

Currently, the use of metamaterials (MMs) to dynamically manipulate the polarization state of terahertz (THz) waves is of great interest for applications such as conveying information and target detection. However, it remains a key challenge to integrate tunable and multiple functions into a single MM device. Based on a 3D Dirac semimetal (DSM)-Teflon-graphene multilayered structure, the propagation performance of the dual-functional polarization converter (DPC) has been investigated in the THz regime, which can achieve cross-polarized reflection or transmission conveniently by adjusting the Fermi level of the graphene inserted into the dielectric space layer. Particularly, at a large Fermi level of 1.0 eV, the proposed DPC realizes a broadband cross-polarized reflection at 0.94-2.17 THz with polarization conversion ratio more than 0.9, and the maximum amplitude modulation depth (MD) of the cross-polarization resonance is 29.2% by adjusting the 3D DSM Fermi level in the range of 0.01-0.15 eV. Meanwhile, if the Fermi level is zero, two obvious cross-polarized transmission peaks can be observed at 1.14 THz and 1.92 THz, and the corresponding amplitude MDs are 49.0% and 62.6% respectively, by varying the 3D DSM Fermi level. Additionally, with a thin layer of 3D DSM as a tunable substrate, the maximum MD amplitude of the cross-polarized reflection curve reaches 52% by changing the Fermi level in the range of 0.01-0.15 eV. These results are very helpful in understanding the tunable mechanisms of 3D DSM plasmonic devices and aiding the design of THz multi-functional devices, such as polarizers, wave plates, and modulators.