Dynamic control of electromagnetically induced transparency based on symmetric and asymmetric phase-change metasurfaces

Dynamic control of electromagnetically induced transparency (EIT) is realized in symmetric and asymmetric phase-change metasurfaces composed of periodic Ge₂Sb₂Te₅ (GST) nanoring array. The symmetric GST nanoring array supports the excitation of tunable magnetic dipole and toroidal dipole resonances. Significantly, the manipulation of either the outer or inner diameter of the GST nanoring enables the magnetic dipole resonance to interact with the toroidal dipole resonance, leading to the formation of EIT, which can be tuned by altering the phase of GST. Additionally, two high-Q quasibound states in the continuum (quasi-BICs) can be induced in the asymmetric GST nanoring array. Furthermore, a high-Q EIT resonance can be achieved through the interaction of a magnetic dipole resonance with a quasi-BIC resonance, or alternatively, through the interaction of a toroidal dipole resonance with another quasi-BIC resonance. The symmetric and asymmetric GST nanoring arrays hold promise for usage in slow-light systems, modulators and reconfigurable filters.