Figure 4.

Dependence of the absorption peak amplitude on dielectric spacer thickness $t_{\mathrm{S}}$ (a) and top nanodisc thickness $t_{\mathrm{T}}$ (b) for both resonance modes. Shaded regions correspond to the critical coupling regime that occurs at $t_{\mathrm{S}-\mathrm{critical}}$ (a) and $t_{\mathrm{T}-\mathrm{critical}}$ (b), resulting in perfect absorption for both resonances. Above $t_{\mathrm{T}-\mathrm{critical}}$ the scattering on the nanodiscs become dominant and absorption decreases. Below and above $t_{\mathrm{S}-\mathrm{critical}}$ the coupling weakens, thus the absorption of the system is reduced.