Fig. 4: Field maps and complex mode structure.

a Experimental (solid blue), simulated (solid dark cyan) and calculated (dashed lines) differential reflection spectra of Bi₂Te₃ metamaterial slit array of length 4.30 μm. The fundamental and second-order resonances at 8.55 and 4.35 μm, respectively, are evident in the plot. The sharp peaks in the simulated and calculated spectra around 4.60 and 6.50 μm are due to diffraction effects. Maps of electric (E) and, magnetic (H) fields determined by FEM simulations showing the nature of the mode at the, b, c fundamental, and d, e second-order resonances. The maps have been calculated over one half of the slit, for simulation size purposes. The cyan outline overlaid on the color maps indicates the full slit and simulation region for clarity. f The contribution of various multipoles to the (displacement) current excitation induced in the metamaterial by the incident wave polarized perpendicular to the slits, including electric dipole (order 0), magnetic dipole (order 1), electric quadrupole (order 1), and toroidal dipole (order 2). g Schematic representation of the various modes in the metamaterial. See Supplementary Note 1 for further details.