A tunable broadband polarization-independent metamaterial terahertz absorber based on VO2 and Dirac semimetal

A broadband tunable metamaterial absorber with polarization and angle-insensitiveness is proposed for terahertz frequencies. The metamaterial design consists of a dielectric layer separating a periodic array of wheel-shaped vanadium dioxide (VO2) inclusions and a Dirac semimetal (DS) backplane. Numerical simulations show that the absorption performance can be flexibly adjusted from 4.3% to nearly 100% by changing the conductivity of VO2, the Fermi energy of DS, the permittivity of the dielectric spacer and the structure's parameters. A 5.37 THz ultra-wideband absorptance over 90% can be achieved from 4.04 THz to 9.41 THz when the permittivity of the dielectric is 1.34 under normal incidence. The impedance matching theory, the Fabry-Perot interference, and the electric field distributions are introduced to discuss the physical mechanisms of the broadband absorption. The upper edge of the absorption band is sensitive to the refractive index of the analyte, and a high sensitivity of 1.94 THz/RIU has been obtained around 4.5 THz. The proposed absorber possesses the advantages of polarization-independence and wide-angle tolerance both for TE and TM waves. The terahertz tunable broadband absorber has potential applications in terahertz energy harvesting, sensing, and modulation.