Broadband and strength-switchable circular dichroism in a GeSbTe-based metasurface.

Circular dichroism (CD) is highly required in the applications of biological detection and analytical chemistry. In this paper, we achieved a giant, broadband, and strength-switchable CD effect in a quadruple -shaped (GST) metasurface. At the amorphous state of GST (a-GST), the giant CD reaches 0.92 and the width of the absorption >0.80 is about 100 nm. The giant and broadband CD originates from polarization selective excitations of Mie resonances and the coupling between subunit resonators. With the transition from a-GST to crystalline GST, CD could be dynamically switched from 0.92 to 0.05. The GST-based metasurfaces with giant and wide-range switching CD will promote the development of active chiral devices.