Free switch between bound states in the continuum (BIC) and quasi-BIC supported by graphene-metal terahertz metasurfaces

Abstract An important topic of modern nanophotonics focuses on the bound states in the continuum (BIC) that the non-radiative localized waves lie within the radiative continuous spectrum, which has been introduced into metasurfaces to construct a strong resonance system. The development of theory and application promotes the advanced physics research on metasurfaces supporting dynamic BIC. However, the dynamic conversion between quasi-BIC and BIC of the metasurfaces is still not realized in strict sense. Herein, we report a significant progress that the free switch between BIC and quasi-BIC is successfully achieved by introducing the structured graphene into the metal terahertz metasurfaces, which is based on free-electron concentration of graphene changing from semiconductor-like to metal-like with adjustment of Fermi energy. We propose the efficient-structure model to explain these phenomena, and prove the wide applicability of this model by investigating seven class metal structures which includes a parameter-tuned metasurface and six common symmetry-protected metasurfaces. The further investigation shows such graphene-metal metasurface array has potential application in dynamic display, and it only needs to change the bias voltage applied on each structure to obtain different display contents, without the requirement of preparing additional metasurface array, which is impossible to achieve via traditional static metasurfaces.