Strong transverse magneto-optical Kerr effect at normal incidence based on hybrid bound states in the continuum

Efficient transverse magneto-optical Kerr effect (TMOKE) at the nanoscale has attracted great interest in recent years due to the highly desirable properties it offers in nonreciprocal photonic devices. Extensive efforts have been made to achieve strong TMOKE based on the efficient absorption of magneto-optical material by using optical resonance with a high Q factor and enhanced electromagnetic field. For a magneto-optical material, however, the efficiency of TMOKE is determined not only by the absorption but also by the spatial symmetry breaking of the magneto-optical material. Here, we propose a dielectric-metal hybrid metasurface composed of a regular array of silicon nanocuboids sitting on a thin metal film. It supports various optical resonances, including Mie resonances, bound states in the continuum (BICs), surface lattice resonances (SLR), and surface plasmon polaritons (SPPs), offering us the opportunity to manipulate the Q factors of optical modes, the intensity and spatial distribution of the electromagnetic field by exploiting the coupling of different optical modes. By virtue of the highly anisotropic electromagnetic field realized by the coupling between the quasi-BIC and the SLR mode, the efficiency of TMOKE at normal incidence can be enhanced by 42%, which is six times greater than that achieved by pure quasi-BIC only. Our method provides insights for designing high-efficiency TMOKE photonic devices, thereby opening up possibilities for their use in a wide range of applications, including magnetic storage devices and nonreciprocal photonic devices.