Controlling optical responses through local dielectric resonance in nanometre metallic clusters

Optical responses in dilute composites are controlled through the local dielectric resonance of metallic clusters. We consider two located metallic clusters close to each other with admittances \varepsilon₁ and \varepsilon₂. Through varying the difference admittance ratio \eta = (\varepsilon _2 - \varepsilon_0 ) / (\varepsilon _1 - \varepsilon _0 ), we find that their optical responses are determined by the local resonance. There is a blueshift of absorption peaks with the increase of \eta. Simultaneously, it is known that the absorption peaks will be redshifted by enlarging the cluster size. By adjusting the nano-metallic cluster geometry, size and admittances, we can control the positions and intensities of absorption peaks effectively. We have also deduced the effective linear optical responses of three-component composites \varepsilon _\rm e = \varepsilon _0\bigl(1 + \sum_n = 1^n_\rm s (\gamma _n_1 + \eta \gamma_n_2 )/(\varepsilon _0 (s - s_n )) \bigr), and the sum rule of cross sections: \sum_n = 1^n_\rm s (\gamma _n_1 +\eta \gamma _n_2 ) = N_h_1 + N_h_2 , where N_h_1 and N_h_2 are the numbers of \varepsilon _1 and \varepsilon _2 bonds along the electric field, respectively. These results may be beneficial to the study of surface plasmon resonances on a nanometre scale.