Fig. 8

a Schematic design of the asymmetric quadrumer with a₁ = 60 nm, a₂ = 80 nm, a₃ = 100 nm, d₁ = 15 nm, d₂ = 10 nm, d₃ = 5 nm, d₄ = 30 nm and h = 40 nm. The black arrow on the top presents the polarization of the excitation and the black dotted line at the middle of the quadrumer shows the symmetry line; b Simulated scattering profile of the asymmetric quadrumer. The magenta and red dotted (vertical) lines indicate the spectral position of the Fano dips at 815 nm and at 880 nm, respectively; c-d NFE maps computed at a plane 1 nm above the top surface of the asymmetric quadrumer at the Fano dips