Multifunctional terahertz metasurface utilizing Dirac semi-metal and vanadium dioxide hybrid metamaterials

Abstract

We have proposed a novel multifunctional terahertz metasurface based on Dirac semi-metal and VO2 hybrid metamaterials that can solve many shortcomings of typical metal-medium-metal electromagnetic metamaterials, such as a narrow band, untunablility and single functionality. By adjusting the conductivity of VO2 and the Fermi energy of the Dirac semimetal, the metasurface can switch between the dual-band perfect absorber and Half Wave Plate (HWP)/Quarter Wave Plate (QWP). Numerical simulation results show that two perfect absorption peaks appear at 4.094 THz and 4.894 THz when vanadium dioxide is in a fully metallic state. Interestingly, the position and value of the two absorption peaks are only slightly effected by the Fermi energy of the resonant structure composed of Dirac semimetal in the middle layer. Moreover, the metasurface switches to a polarization converter, and it is worth noting that the metasurface can switch between QWP and HWP as the Fermi energy moves from 85 meV to 180 meV when VO2 is in an insulating state. A broadband perfect QWP has been obtained when the Fermi energy of Dirac semimetal is 85 meV, which can transform an incident linearly polarized wave to Left-handed circularly wave with an ellipticity greater than 0.95 in the frequency range of 1.71–2.73 THz. Moreover, the functionality of the metasurface switches from QWP to HWP when the Fermi energy of Dirac semimetal increases to 180 meV. This change can transform the incident linearly polarized wave to its orthogonal polarized wave with polarization conversion ratio exceeding 0.95 and a bandwidth of 1.06 THz in the frequency range of 1.82–2.88 THz. In addition, we practically investigated the influence of the incident angle to verify the potential of the designed metasurface. Such a multi-functional, broadband and high-performance metasurface has excellent application potential in sensing, imaging and super lenses.