Switchable high-Q electromagnetically induced transparency based on the Ge2Sb2Te5 nanodisk dimers

Abstract

Bound states in the continuum (BICs) based on metasurfaces have gained significant attention recently to enhance the strength of light-matter interaction. However, most BIC metasurfaces possess fixed optical properties once they have been fabricated. In this study, we introduce the concept of BICs to the phase-change metasurfaces composed of Ge2Sb2Te5 nanodisk dimers. The Ge2Sb2Te5 nanodisk dimers can support a low-Q transverse magnetic dipole resonance, a high-Q toroidal dipole resonance and a high-Q longitudinal magnetic dipole resonance. By adjusting geometric parameter, the high-Q longitudinal magnetic dipole resonance can be converted into a BIC mode. Notably, when Ge2Sb2Te5 is in the amorphous phase, high-Q electromagnetically induced transparency (EIT)-like resonances can be achieved due to the interaction between a low-Q transverse magnetic dipole mode and either a high-Q toroidal dipole mode or a high-Q longitudinal magnetic dipole mode. However, the EIT resonances are switched off when Ge2Sb2Te5 is transformed into the crystalline phase. Furthermore, the high-Q EIT resonances enable the realization of an ultrahigh group refractive index, and can be tuned through the phase transition of Ge2Sb2Te5. The switchable high-Q EIT resonances hold potential applications in slow-light devices, optical modulators, and biosensors.