Tristate Switching of Terahertz Metasurfaces Enabled by Transferable VO2

Achieving dynamic switching among absorption (A), reflection (R), and transmission (T) states is not only essential for advancing the understanding of light-metasurface interactions but also holds significant potential for practical applications, such as selective electromagnetic shielding and smart windows. However, at terahertz and higher frequencies, implementing active elements in multilayer configurations presents challenges that are not as straightforward as those encountered in the microwave range. In this work, it is demonstrated that tristate ART tuning can be realized in a single-layer, free-standing metasurface by switching between a dual dipolar mode (electric dipole and magnetic dipole) and a single dipole mode (electric dipole). By transferring a flexible vanadium dioxide (VO₂) thin film onto the free-standing dielectric Huygens’ metasurface, ART modulation is achieved, transitioning from a near-unity transmission state to a near-perfect absorption state, and finally to a high-reflection state with the reflection up to 0.65 during the insulator-to-metal transition induced by heating onto the phase-change material. The results may lead to new approaches in designing reconfigurable metasurfaces based on phase-change materials for wavefront control and electromagnetic shielding applications.