(a) Schematic diagram of a coupled structure with length, width, and height for small Au rod being L_S = 55 nm, W_S = 10 nm, H_S = 10 nm, and for big Au nanorod being L_B = 150 nm, W_B = 50 nm, H_B = 50 nm, respectively, and gap size being 15 nm. (b) Absorption cross section of individual small nanorod, individual big nanorod, and small nanorod in the coupled structure. (c) Extinction cross section of individual small Au nanorod, individual big Au nanorod, and coupled structure.