Wavelength-tunable high-Q circular dichroism based on the hybrid chiral phase-change metasurface

Chiral metasurfaces have experienced significant advancements over the past decade in enhancing chiral light-matter interactions. However, the functions of most chiral metasurfaces remain static post fabrication. Here, we present a wavelength-tunable high-quality (Q) circular dichroism (CD) by integrating a chiral metasurface with the phase-change material Ge₂Sb₂Te₅ (GST). The hybrid chiral metasurface exhibits a pronounced CD response when GST is in its amorphous state, with the operating wavelength being modulated as GST transitions to its crystalline state. The metasurface can support a bound state in the continuum (BIC) under conditions where the structure exhibits both in-plane mirror and inversion symmetries. By adjusting the geometric parameter to simultaneously break the in-plane mirror and inversion symmetries, the BIC is turned into a chiral quasi-BIC characterized by a high-Q factor in the CD spectrum. Furthermore, the wavelength of the chiral quasi-BIC can be dynamically tuned through the GST phase transition. This wavelength-tunable high-Q hybrid chiral metasurface holds potential applications in chiral sensing, active circular polarizers, and tunable nonlinear enhancement.