Thermally tunable terahertz switchable quad-band to broadband absorption induced by Mie–plasmon coupling

Metamaterials enabling on-demand switchable terahertz (THz) absorption functionalities are essential for advancing multifunctional integrated photonic devices. However, most existing tunable designs rely on fine-tuning a single dominant resonance mode. This physical mechanism limits their functionality primarily to frequency shifting or intensity modulation, making it difficult to achieve distinct switchable operation between different operating modes. To address this, we propose a vertically integrated VO₂–dielectric microsphere hybrid metasurface absorber. It utilizes the insulator-to-metal transition (IMT) of VO₂ to actively control the coupling between the top-layer VO₂ plasmon resonance and the bottom-layer ZrO₂ microsphere Mie resonance. In the insulating state of VO₂, the coupling is disabled, and the device is dominated by Mie resonances, exhibiting an efficient quad-band absorption mode with each peak absorptivity exceeding 95%. When VO₂ transitions to its metallic state, the coupling is activated, allowing the top-layer plasmon resonance to couple with the bottom-layer Mie resonances. This interaction induces a spectral reconfiguration that merges the discrete high-frequency resonance peaks into a continuous broadband absorption band (0.919–1.157 THz) with an absorptivity exceeding 90%, thereby realizing switchable performance from quad-band to broadband absorption. This design strategy provides a new physical paradigm for realizing intelligent metamaterials with switchable functionalities.