Thermally Tunable Quasi-Bound State in the Continuum and Electromagnetically Induced Transparency Analogue Based on...

Metasurfaces supporting bound states in the continuum (BICs) offer ultrahigh-Q resonances, yet their integration with active tuning mechanisms and mode coupling phenomena remains largely unexplored. In particular, a tunable quasi-BIC-mediated electromagnetically induced transparency (EIT)-like effect using phase-change materials is still an open challenge. Here, we present both numerical and experimental demonstrations of tunable quasi-BIC and EIT-like resonances by integrating asymmetric metasurfaces with the phase-change material Ge₂Sb₂Te₅ (GST). By breaking the in-plane inversion symmetry, a BIC mode is converted to a quasi-BIC mode. Furthermore, EIT-like resonances arise from the coupling between localized surface plasmons and either an electric dipole or quasi-BIC, leading to a dual EIT-like effect with distinct physical origins. The incorporation of GST enables thermal modulation of both quasi-BIC and EIT-like resonances through a phase transition from the amorphous to the crystalline phases, resulting in pronounced changes in transmission amplitude and electromagnetic fields. The hybrid phase-change metasurfaces hold potential for applications in terahertz modulators, filters, and slow-light devices.