Tunable metasurfaces based on phase-change materials

Due to their superior ability to control light, metasurfaces, ultrathin two-dimensional metamaterials composed of subwavelength nanostructures, have attracted great attention in recent years. Exploring geometric and material freedom in designing elementary nanostructures and their ambient environment of metasurfaces enables versatile optical devices, such as planar metalenses, holographic imaging and thermal radiators. With phase-change materials (PCMs) such as GeSbTe and VO2 integrated into metasurfaces, the optical functionalities of metasurfaces can be flexibly tuned by exploiting the phase transitions of PCMs induced by external stimuli, thereby opening up new directions and perspectives for dynamic tunable metamasurfaces. In this article, we review the recent progress of tunable metasurfaces based on PCMs, analyze their underlying working mechanisms and highlight their important applications. We conclude this review by bringing our perspectives on challenges and future directions in this field.