Hsiao H.-H.Liu A.-Y.HUI-HSIN HSIAO2022-09-192022-09-192022https://www.scopus.com/inward/record.uri?eid=2-s2.0-85123468260&doi=10.1002%2flpor.202100404&partnerID=40&md5=1fe8575732ca4308d415ba5600300a3bhttps://scholars.lib.ntu.edu.tw/handle/123456789/621088Dynamic toroidal dipole (TD) with its peculiar characteristic of broken space-inversion and time-reversal symmetries plays an important role in the fundamental physics of light–matter interaction. Here, TD metamaterials comprised of amorphous silicon nanopillar arrays embedded in spin-on-glass layer are experimentally demonstrated. Upon normal incidence of plane wave, the transverse toroidal moment and the associated anapole-like state are excited in optical regime. The strong TD response stems from a complete head-to-tail configuration of the magnetic dipole moments within each individual nanopillar. Both the experimental and simulation results show that such TD mode sustains a large structural tolerance and can be spectrally tuned by elongating the cylindrical axis perpendicular to the light polarization, corresponding to a cross-sectional variation from circular to elliptical shapes. The excited TD mode is found to exhibit ultrahigh refractive index sensitivity compared to other multipoles, resulting in a sensitivity of 459 nm (470 nm) per external refractive index change in the experiment (calculation). This approach provides a simple and straightforward path in realizing toroidal metamaterials and establishes a new flat-optics platform for realizing active metadevices, sensors, and nonlinear nanophotonics. © 2022 Wiley-VCH GmbHanopole mode; dielectric metasurfaces; Mie resonances; refractive-index sensing; toroidal dipole[SDGs]SDG12Amorphous silicon; Excited states; Light; Refractive index; Spin glass; Dipole mode; Fundamental physics; Light-matter interactions; Nanopillars array; Optical-; Silicon nanopillars; Spin-on-glass; Time reversal symmetries; Toroidal modes; Ultrasensitive; Metamaterialsjournal article10.1002/lpor.2021004042-s2.0-85123468260