Fig. 4: Ring resonators array embedding vdW topological insulator heterostructures.
From: Second and third harmonic generation in topological insulator-based van der Waals metamaterials
a Bi-dimensional map of the normalized electric field (ESSRR/E0) on the Bi2Se3 SSRR at the resonance frequency νSIM ~ 3.245 THz, calculated using FEM simulations on a SSRR fabricated on as-grown Bi2Se3 heterostructures. E0 is the electric field on the bare sapphire surface. b Simulated optical transmittance of the design shown in (a), extracted when the polarization of the input beam is parallel to the split gap dipole. c SEM images acquired on the SSRR fabricated on the (InxBi(1−x))2Se3/Bi2Se3/(InxBi(1−x))2Se3 sample, H2. d Experimental transmittance acquired on the sample shown in (c), using FTIR, under vacuum, with a spectral resolution of 1 cm−1, employing internal MIR (Globar) source and a helium-cooled Si bolometer. A rotating, wire-grid linear polarizer was positioned in front of the sample; the reported transmittance curve was obtained by taking the ratio of the curve acquired by selecting the linear polarization parallel to the split gap dipole (polarization angle 0°), with the one acquired at 90°, and then normalizing to account for the reflection losses of the sapphire substrate (~40%). e Normalized electric field (EDSRR/E0) map of the Bi2Se3 DSRR at the resonance frequency νSIM ~ 3.25 THz, calculated using FEM simulations for the array realized directly on the as-grown MBE Bi2Se3 sample. f Simulated optical transmittance of the design shown in (e), extracted when the input beam polarization is oriented parallel to the split gap’s dipole. g SEM images acquired on the DSRR fabricated on the (InxBi(1-x))2Se3/Bi2Se3/(InxBi(1−x))2Se3 sample, H2. h Experimental transmittance acquired on the sample shown in (g), using the same methods as (d)
