Fig. 1. Illustration of the excitation of the (a) electric and (b) magnetic anapole states. The surface charge distributions of the silver trimer and nonamer at the wavelength of the electric and magnetic anapole states suggest the multipole configurations. The dark green ring shows the head-to-tail Cartesian ETD moments.

Fig. 2. Scattering cross sections and their spherical multipole decomposition calculated for the silver trimers. (a) Schematic of the silver trimer that consists of three same-sized nanodisks with the radii r=61  nm. The thickness of three silver disks is 40 nm, and the incident angle θ=80°. (b) Evenly spaced three silver nanodisks with the gaps g1=g2=20  nm; (c) g1=10  nm, g2=20  nm; (d) g1=5  nm, g2=20  nm.

Fig. 3. Spherical ED, Cartesian ED, Cartesian ETD scattering cross sections, and the phase of Cartesian TD and Cartesian ETD moments with the corresponding electric near-field distributions of the silver trimers at the dips of spherical ED spectra. (a) g1=20  nm, (b) g1=10  nm, (c) g1=5  nm, respectively. The white arrows indicate the directions of the E-field.

Fig. 4. Normalized multipole scattering power of (a) the silver trimer and (b) the nonamer. The insets are the structure schematics; for the trimer, the radii of the three silver nanodisks are 61 nm with the gap of 16 nm between adjacent ones. The silver nonamer is formed by adding two small nanodisks around every disk of the trimer with the radii of 56 nm and the gap of 10 nm between adjacent ones. The gaps between the small nanodisks and the closest nanodisks of the trimer are 8 nm. The MD emitters are set in the center of the trimer and nonamer with the orientation along the z axis, respectively.

Fig. 5. Contributions of the normalized spherical MD and Cartesian MD and MTD to the radiative powers with the corresponding electric near-field distributions through the center of the silver nanodisks (a) at 590 nm for the trimer and (b) at 590 nm for the nonamer.

Fig. 6. Radiative power transferred into the far field from an MD emitter placed in the center of the (a) silver trimer and (b) nonamer, respectively.