Broadband Mid‐Infrared Absorber Based on Dirac Semimetal Metamaterials

Abstract

In this paper, a broadband terahertz absorber based on the Dirac‐semimetal AlCuFe is proposed. A classic metal–dielectric–metal (MIM) sandwich structure is adopted, consisting of a periodic AlCuFe pattern on the top, a silica dielectric spacer in the middle, and a gold reflective film at the bottom. When the Fermi level of the top AlCuFe layer is set to 65 meV, the absorber exhibits absorptance above 90% over a bandwidth of 10 THz in the range of 21.5–31.5 THz, with near‐perfect absorption peaks at 22.7 and 30.8 THz. Electric field analysis and equivalent impedance theory reveal that the broadband strong absorption originates from the synergistic coupling between localized electromagnetic resonances and guided‐mode resonances (GMR). A systematic study of the key geometric parameters—the spacer thickness H2, the unit‐cell period P, and the pattern dimensions—shows that the spacer thickness is the most sensitive parameter in terms of fabrication tolerance. In addition, the absorber exhibits excellent polarization insensitivity and maintains relatively stable performance for incident angles up to 30°. Owing to the tunable Fermi level of AlCuFe, the low‐ and mid‐frequency absorption peaks exhibit a monotonic blueshift with increasing Fermi level, endowing the device with dynamic modulation capability. In summary, the proposed absorber integrates broadband absorption, polarization insensitivity, and dynamic tunability, showing significant research value and application prospects for mid‐infrared optoelectronic devices.