Spatially decoupled Dirac semimetal and Vanadium dioxide metasurface for quad-mode Terahertz absorption

Abstract

To overcome the fixed-band limitations of conventional terahertz (THz) absorbers, we propose a spatially decoupled, quad-mode tunable metasurface absorber integrating bulk Dirac semimetal (BDS) and vanadium dioxide (VO2). By synergistically modulating the temperature-driven phase transition of VO2 and the Fermi energy of BDS, the device achieves flexible switching among broadband, single-, dual-, and triple-band absorption modes. Specifically, these diverse functional absorption scenarios are realized by independently regulating the bias voltages applied to the distinct layers of the BDS structure to dynamically alter their Fermi levels. When VO2 is in the metallic state, the absorber exhibits efficient broadband absorption (>90%) across the 3.56–7.31 THz range. When VO2 is in the insulating state, discrete single- (7.36 THz), dual- (4.30/8.66 THz), and triple-band (4.36/7.36/8.82 THz) absorption peaks with near-unity absorptivity can be precisely excited. Notably, enabled by the spatial and spectral complementarity between the top and intermediate BDS layers, the device demonstrates a unique "dual-track tuning" mechanism, allowing the central resonance frequency and flanking resonances to be reconfigured independently without mutual interference. Furthermore, the absorber features excellent polarization insensitivity and maintains high absorptivity under oblique incidence up to 50°. This study provides a vital structural paradigm and theoretical guidance for developing highly integrated, multi-mode dynamically reconfigurable THz devices.