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The tunable propagation properties of 3D Dirac semimetal (DSM) patterned metamaterial (MM) structures have been symmetrically investigated in the terahertz (THz) regime. The results demonstrate that the resonant properties are very sensitive to the thicknesses of DSM MMs, and hundreds of nanometers are required to excite strong resonant curves. The DSM MMs support both strong LC and dipolar resonances, quite different from graphene MM patterns which mainly depend on dipolar resonance. As the Fermi level increases, the resonant strength becomes stronger, and significant modulation can be achieved, e.g. the amplitude and frequency modulation depths of transmission curves are more than 99% and 80%, respectively. In addition, by utilizing asymmetrical resonators, a very sharp Fano resonant peak is achieved with a large Q-factor of more than 25, for which the figure of merit is about 20. The results are very helpful to understand the tunable mechanisms of DSM devices and design novel THz plasmonic components, such as modulators, filters, and sensors.

Based on SrTiO3 (STO) elliptical metamaterials (MMs) structures, the tunable propagation properties have been systematically investigated in the THz regime, including the effects of temperatures, incident angles, operation frequencies, and graphene Fermi levels. The results reveal that STO MMs manifest excellent thermally tunable properties, e.g. the amplitude and frequencies modulation depths are larger than 95.3% and 21.8% if temperature varies in the range of 70-320 K. The incident angles affect the resonant curves significantly, the amplitude modulation depth approximates 90% by changing the polarization angles, and the Q-factor reaches more than 20. The tunable Fano resonances can be achieved by utilizing a symmetrical STO-graphene structure. If the graphene Fermi level changes in the range of 0.3-1.0 eV, the amplitude modulation depth of transmission curve is more than 80%. The results are very helpful to understand the resonant mechanisms of ferroelectric metamaterials and design novel high Q-factor devices in the future, e.g. sensors, modulators, and filters.

By integrating the graphene layer with the dielectric loaded surface plasmon waveguides, the tunable propagation properties have been investigated in the near-IR region, including the influences of operation frequency, the Fermi level of the graphene layer, and dielectric layer thickness. To improve the modulation properties, multiple unit cell (graphene-Al2O3) structure has been adopted. The results manifest that as the period number of the unit cell increases, the modulation depths of the propagation properties increase obviously. For instance, the modulation depth of propagation length can reach about 80% if the Fermi level changes in the range of 0.1–0.5 eV. As frequency increases, the effective index of the hybrid mode increases, while the propagation length shows a peak. The results are very helpful in understanding the tunable mechanisms of graphene plasmonic devices and designing novel waveguide structures, e.g. resonators and modulators.