Kerker Effects and Bound States in the Continuum in PT-Symmetric Dielectric Metasurfaces

We investigate the light transmission and reflection spectra of parity-time (PT) symmetric dielectric metasurfaces composed of high refractive index nanostructures with in-plane gain-loss modulation through the scattering matrix and semianalytical Cartesian multipoles methods. We find that the Kerker effects, i.e., the strong forward-to-backward asymmetric scattering originating from overlapping the electric and magnetic multipolar resonances, can be tailored by the gain and loss. In addition, we observe another kind of high-Q resonances, i.e., quasi-bound states in the continuum which couple to the electric and magnetic multipolar radiations, in the transmission and reflection spectra with different incident polarizations lights by manipulating the gain and loss in the metasurfaces. Our results suggest the ways to achieve Kerker effects and engineer the resonances in non-Hermitian metasurfaces for many practical applications in nanophotonics.