Circularly polarized light detection via toroidal resonance using an X-shaped chiral metasurface

Toroidal dipole resonance has been extensively utilized in dielectric or plasmonic nanostructures due to its notable properties, including effective mode confinement with reduced radiation loss and effective near-field localization. However, typical nanostructures that support toroidal dipoles have exhibited symmetric geometry so far, and, thus, the selective excitation of circularly polarized states in such toroidal resonance remains largely unexplored. Here, we incorporate the chiral geometry with the toroidal dipole to realize an efficient chiral metasurface with highly selective light absorption. We reveal how the phase of the magnetic toroidal dipole (MTD) is effectively controlled by optimally incorporating geometric chirality in the proposed X-shaped nanostructures. Through both simulations and experimental validation, we demonstrate that right-handed circular polarization induces strong MTD resonances, contrary to left-handed circular polarization, which results in significantly weaker responses due to destructive interference of toroidal dipole modes. Furthermore, we design the proposed metasurface as a nanobeam array format to extract circularly polarized light selective photocurrent, which offers the potential integration into compact, polarization-sensitive devices for the applications of biosensing, quantum optics, and polarimetric imaging.