Bi-tunable terahertz absorber based on strontium titanate and Dirac semimetal

Abstract

We proposed a polarization-insensitive absorber based on strontium titanate (STO) and bulk Dirac semimetal (BDS) in the terahertz (THz) region. The center frequency of the absorption peak can be independently regulated by temperature or Fermi energy level of STO or BDS, respectively. The numerical simulation result reveals that the peak absorptivity reaches to 99.98% at 2.16 THz when the temperature and Fermi energy were set at 300 K and 20 meV, respectively. Interestingly, by adjusting the temperature of STO from 250 to 400 K, the simulation results indicate that the center frequency can be tuned from 1.94 to 2.53 THz, and peak absorptivity can be maintained above 99% at normal incident. As the Fermi energy EF of Dirac semimetal increases from 10 to 60 meV, the center frequency can be changed from 2.14 to 2.44 THz and the amplitude of absorption peaks can be tuned from 99.9% to 82.8%. Impedance matching theory was used to understand the tunable performance. Furthermore, interference theory was employed to further explain the absorption mechanism of the proposed absorber. The absorber achieves bi-controlled absorptance via two independently controllable methods, which may provide guidance to research tunable, smart and multifunctional terahertz devices.

Terahertz Metamaterial Absorbers

“…Xiong et al used STO as the dielectric layer material (temperature sensitive material) and BDS as the resonator material on the top layer (Figure 12d). [97] BDS has higher electron mobility and stability compared with graphene, which is more suitable for the TMA fabrication. Unlike the performance of VO 2 , the permittivity of STO makes the absorption peak blue shift as the temperature increases.…”

“…i) Multi-field tunable TMA. Reproduced with Permission [97]. Copyright 2020, Optical Society of America.…”

“…d) Schematic diagram of the TMA with BDS and STO, and simulated absorption spectra e) with increasing temperature and f) with increasing Fermi energy of BDS. Reproduced with permission [97]. Copyright 2020, Optical Society of America.…”

3D Dirac Semimetal Supported Tunable TE Modes

“…[19][20][21][22][23][24] The complex conductivity of DSM layer embraces the contributions of intraband and interband transitions, which can be regarded as an analogue of Drude conductivity and a direct electronic transitions from the lower valence band to the upper conduction band, respectively. [25][26][27][28][29][30][31] Because of the gapless electron energy property, the interband transition is enhanced and DSM layer indicates obvious dielectric responses. Thus, besides common intraband transition usually existed in conventional plasmonic system, DSM also supports transverse electric (TE) plasmon mode.…”

“…Compared with graphene layer, 3D DSM also inhibits the advantages of higher mobility, more stable, and less susceptible to environmental defects. [27][28][29][30][31][32] 3D DSM also surmounts the restriction of thickness and gives an additional degree-of-freedom in the construction of functional devices. Furthermore, TE plasmonic mode is much stronger and convenient to achieve from experimental viewpoints, resulting from much larger thickness of 3D DSM layer compared with graphene.…”