Switchable ultra-broadband to multi-frequency THz absorption in a VO ₂ -graphene hybrid metamaterial

The development of reconfigurable terahertz (THz) photonics has been constrained by the inability to dynamically control the spectral response without compromising performance. Here, we overcome this by introducing a hybrid graphene-vanadium dioxide (VO 2 ) metasurface that enables active, on-demand switching between ultra-broadband and multi-frequency resonant absorption. Through a systematic analysis of material permittivity, we identify the optimal combination of materials to achieve this dual functionality—in its broadband state, the structure exhibits ultra-broadband performance: over 90% absorption spanning 2.18–13.80 THz, which corresponds to a 145.43% relative bandwidth—the highest reported for a THz absorber—with a remarkable 98.91% average absorption. By electrostatically tuning the graphene’s Fermi level, we reconfigure the system to generate two discrete, strong absorption peaks at 6.86 THz and 9.58 THz, respectively. This dual functionality arises from a coupled interplay between the phase transition in VO 2 and gate-tunable plasmonic response in graphene, facilitating near-perfect impedance matching across an unprecedented bandwidth. Furthermore, the metamaterial exhibits robust insensitivity to ±4% structural imperfections, maintaining a flat, near-unity absorption profile with only minor degradation at lower frequencies. Featuring polarization insensitivity and wide-angle stability, our platform establishes a new paradigm for adaptive terahertz systems, with transformative implications for imaging, sensing, and adaptive communications.