Modulation of anisotropic middle layer on the plasmon couplings in sandwiched gold nanoshells

The influence of the spherical anisotropy (SA) of a middle layer on the plasmon resonance couplings in the sandwiched gold nanoshell (Au/SA/Au) has been investigated by means of a modified Mie theory. It is found that the plasmon couplings in the Au/SA/Au nanoshells are more sensitive to the permittivity along the radial direction of SA layer than the permittivity along the tangential direction. With increasing the anisotropic value of the middle layer, the dipole peaks of antisymmetric ω mode and symmetric ω + mode both show blue-shifts, while the shift of the antisymmetric ω mode is larger than that for the symmetric ω + mode. The larger anisotropic value of the SA layer induces the stronger near-field outside the nanoparticles for the antisymmetric ω mode, while the smaller anisotropic value makes the larger near-field for the symmetric ω + mode. We further have found that the middle SA layer with smaller anisotropic value is helpful to obtain larger electric fields inside the nanoshells, which may be useful for their potential applications in nonlinear optics.