A numerical and theoretical study is presented on the realization of the tunable plasmon-induced transparency (PIT) effect in Dirac semimetal films (DSFs) that are known as “three-dimensional graphene”. The weak hybridization between the two parallel bright modes leads to the novel PIT optical response. The properties of the PIT system can be controlled by adjusting the geometric parameters of the DSF strips. Meanwhile, the resonant frequency of the PIT can be dynamically tuned by varying the Fermi energy of the DSFs instead of refabricating the structures. Correspondingly, by adjusting the Fermi energy of the DSFs, a large group delay of more than 1.86 ps is obtained in the vicinity of the transparency peaks. Such proposed DSFs-based PIT system may open up avenues for tunable terahertz switching, slow-light devices, sensing technology and some other THz devices.

We present a bifunctional polarization converter based on Dirac semimetals (DSMs) and vanadium dioxide (VO₂), which consists of two layers of DSMs on both sides, a metal grating and a VO₂ board. The polarization converter frequency is dynamically tuned by changing the Fermi energy level of the DSMs. The result suggests that when VO₂ is in an insulated state, the device behaves as a transmissive polarization converter. The dual-band transmissive polarization conversion and asymmetric transmission (AT) function of circularly polarized (CP) waves are realized at 1.99 THz and 3.46 THz, with the polarization converter ratio (PCR) reached 97.6% and 95.8%, respectively. In addition, when VO₂ is in the metal state, the designed polarization converter is a reflective device, which can maintain the chirality of the reflected CP wave to the incident wave in a wide band. The polarization-maintaining ratio (PMR) in the range of 2 THz to 3.55 THz is higher than 88%. When the angle of incidence is less than 60°, the frequency band of the PMR is narrowed and the amplitude reaches more than 90%.

A bi-tunable triple-band metamaterial absorber based on Dirac semimetal films (DSFs) and vanadium dioxide (VO₂) is presented. When VO₂ is in the fully metallic state, the proposed absorber presents three distinctive absorption peaks in the terahertz range with absorptance 97%. Because the conductivity of VO₂ changes from 100000 to 10 S/m, the reflectance and absorptance intensities achieve dynamic tunability at the three absorption peaks, and the proposed triple-band absorber exhibits a switchable function by the insulation-to-metal transition of VO₂. Moreover, the frequencies of the three absorption peaks can also be tuned by varying the Fermi energies of the DSFs.

To synthesize dynamically tunable bound states in the continuum (BIC) metasurfaces in the terahertz (THz) band, in this study, a Dirac semimetal metasurface was designed for dynamic switching between THz-band BIC and quasi-BIC. We have simulated the designed metasurface, a symmetry-protected BIC with a quality factor (Q-factor) of 147 was achieved by breaking the symmetry of the structure, the variation law of the Q-factor with the asymmetry parameter was investigated, and the physical mechanism of quasi-BIC generation was determined by analyzing the surface electric field and surface current. Notably, the dynamic transition from BIC to quasi-BIC was achieved by varying the Fermi level of the Dirac semi-metal, with the maximum transmission difference of 0.61 and an almost constant resonant frequency for Fermi levels ranging from 2–20 meV. In addition, we fabricated and demonstrated a dynamic near-field display array, wherein different content is dynamically displayed by successively applying different gate voltages. This paper presents a novel design concept for dynamic switching between BIC and quasi-BIC on a metasurface and promotes the practical application of BIC metasurfaces.

We demonstrated a dynamically controlled broadband terahertz (THz) metamaterials absorber, which composed of continuous vanadium dioxide (VO₂) film, a silicon dioxide (SiO₂) layer, and a structured borophene layer. When VO₂ is in its metallic state and the armchair direction of borophene along x axis, the proposed absorber realizes an absorptivity peak value of 100% at 7.2 THz for y polarized normal incidence, and an absorptivity peak value of 79% at 8.9 THz for x polarized normal incidence. It is the anisotropic property of borophene that results in the absorptivity difference for x and y polarization in the whole frequency range. Simulated electric field distribution and surface current oscillation has been extracted to explain the physical mechanism of THz wave absorption. Through modifying the geometric parameters of metamaterials microstructure, the broadband absorption performance can be tailored passively. Additionally, the proposed metamaterials absorber has been actively controlled by manipulating the carrier density of borophene and the conductivity of VO₂, respectively. The absorptivity can be switched from 45% to 100% at 7.2 THz by changing the carrier density of borophene, and from 22% to 100% at 7.2 THz by changing the conductivity of VO₂. Moreover, the proposed absorber exhibits an excellent operation tolerance for oblique TE and TE polarized incidence from 0° to 60°. This work provides a novel approach to design dynamically controlled broadband THz absorbers, which reveals promising applications in the devices of optoelectronic switches, cloakings, filters, and sensors, etc.