Nonvolatile switchable dual-functional THz metamaterial with selective transmission and adjustable absorption empowered by q-BICs

The integration of tunable characteristics and dual functions into a single terahertz (THz) metamaterial is quickly becoming a major focus of research. This paper presents a nonvolatile switchable dual-functional THz metamaterial with selective transmission and adjustable absorption based on quasi-bound states in the continuum (q-BICs), where the q-BICs are achieved through periodically arranged silicon disks tetramer. By introducing asymmetry perturbation through manipulating the radii of diagonal silicon disks of the proposed THz metamaterial, resulting in the transition from symmetry-protected bound states in the continuum (SP-BICs) to q-BICs. When the middle layer Ge₂Sb₂Te₅ (GST) is in the amorphous state, selective transmission is achieved, which can be applied as a bandstop filter. Additionally, by transforming the phase of GST into the crystalline state in the way of heating, the proposed THz metamaterial behaves as an adjustable absorber due to the generations of q-BICs and Fabry-Pérot resonance (FPR) mode. Multipole decomposition and temporal coupled-mode theory (CMT) are applied to explain the underlying physics. Our work provides valuable insights into the integration of the nonvolatile switchable and dual-functional THz metamaterials empowered by q-BICs.