All-dielectric Si metamaterials with electromagnetically induced transparency and strong gap-mode electric field enhancement

We designed all-dielectric π-shaped Si metamaterials and numerically demonstrated their electromagnetically induced transparency (EIT) behavior. Each unit of the metamaterial comprises one horizontal Si nanobar and two vertical Si nanobars with feed-nanogaps between them. A narrow EIT peak with a transmittance of 99% and a Q-factor of 2436 is observed due to the destructive interference between the horizontal bright and vertical dark mode resonators. The EIT can be tunable by changing the nanogap width, and the narrowest EIT window with the largest Q-factor is obtained as the nanogap width is 20 nm. Strong electric field enhancement exceeding 10⁴ in magnitude is also realized inside the 20-nm nanogap. Theoretical fittings according to the coupled Lorentz oscillator model exhibit a well consistency with the simulation spectra, validating the accuracy of the numerical simulation. The designed metamaterial is sensitive to the surround refractive index change with a figure-of-merit of 460, which far exceeds Fano-resonant plasmonic metal sensors. The designed Si metamaterial with a sharp EIT response and a strong electric field enhancement is an ideal platform for applications in optical sensing, low-loss slow-light devices, fluorescence enhancement, and nonlinear optics.