Characteristics and mechanism analysis of Fano resonances in -shaped gold nano-trimer**Project supported by the National Natural Science Foundation of China (Grant Nos. 61320106014, 61675104, and 11474041), the Open Fund of Key Subject of Zhejiang Province, China (Grant Nos. xkzwl12, xkzwl1521, and xkzwl1522), and Ningbo University, China.

Abstract

Fano interference of metallic nanostructure is an effective way to reduce the irradiation loss and improve the spectral resolution. A Π-shaped gold nano-trimer, which is composed of a gold nanorod and two gold nanorices, is presented to investigate the properties of Fano resonances in the visible spectrum by using the finite element method (FEM). The theoretical analysis demonstrates that the Fano resonance of the Π-shaped gold nano-trimer is attributed to the near-field interaction between the bright mode of the nanorice pair and the dark quadrupole mode of the nanorod. Furthermore, by breaking the geometric symmetry of the nanostructure the line-shape spectrum with double Fano resonances of Π-shaped gold nano-trimer is obtained and exhibits structure-dependent and medium-dependent characteristics. It is a helpful strategy to design a plasmonic nanostructure for implementing multiple Fano resonances in practical applications.