Fig. 1. Working principle. (a) Schematic of the hybrid Al/GST dumbbell aperture array. (b) Unit cell of the hybrid Al/GST dumbbell aperture array. (c) Schematic transmission spectra of both symmetric and asymmetric hybrid Al/GST dumbbell aperture arrays through the phase transition of GST.

Fig. 2. Simulated results for the symmetric and asymmetric aluminum dumbbell aperture arrays. (a) Unit cell of the aluminum dumbbell aperture array. (b) Calculated transmission spectra of the aluminum dumbbell aperture array with varying radii r2. (c) Q-factors of the quasi-BIC with varying radii r2. Scattered powers associated with different multipole moments with r2=30  μm for (d) and r2=50  μm for (f). (e) Electric field, surface current, and magnetic field distributions at 0.5 THz for r2=30  μm. (g) Electric field, surface current, and magnetic field distributions at 0.398 THz for r2=50  μm. The directions of current are indicated by the red arrows, while the directions of magnetic field are indicated by the white arrows.

Fig. 3. Simulated results for the symmetric hybrid Al/GST dumbbell aperture array. (a) Unit cell of the symmetric hybrid Al/GST dumbbell aperture array. (b) Calculated transmission spectra of the symmetric hybrid Al/GST dumbbell aperture array at varying conductivities. (c) Scattered powers associated with different multipole moments with σ=100  S/m. (d) Scattered powers of different multipole moments as a function of GST conductivity at 0.497 THz. (e) Electric field, surface current, and magnetic field distributions at 0.497 THz for different conductivities. The directions of current are indicated by the red arrows.

Fig. 4. Simulated results for the asymmetric hybrid Al/GST dumbbell aperture array. (a) Unit cell of the asymmetric hybrid Al/GST dumbbell aperture array. (b) Calculated transmission spectra of the hybrid Al/GST dumbbell aperture array with different radii r2 for σ=100  S/m. (c) Calculated transmission spectra of the asymmetric Al/GST dumbbell aperture array at different conductivities of GST with r2=50  μm. (d) Scattered powers associated with different multipole moments for r2=50  μm and σ=100  S/m. (e) Electric field, surface current, and magnetic field distributions at 0.396 THz for different conductivities, where r2 is chosen as 50 μm. The directions of current are indicated by the red arrows.

Fig. 5. Experimental results. (a) and (b) are the optical microscopy images of the aluminum dumbbell aperture arrays with r2=30 and 50 μm, respectively. The scale bar is 200 μm. (c) Measured transmission spectra of the aluminum dumbbell aperture arrays with varying r2. (d) Measured transmission spectra of the hybrid Al/GST dumbbell aperture arrays with varying r2 at 25°C. Measured transmission spectra of the hybrid Al/GST dumbbell aperture arrays at various temperatures with r2=30  μm for (e) and r2=50  μm for (f). (g) Transmittance at 0.486 THz as a function of temperature for r2=30  μm. (h) Transmittance at 0.352 and 0.483 THz as a function of temperature for r2=50  μm.