Plasmonic coupling in transversely shifted symmetric Au nanocube trimer: New coupling mechanism and plasmonic scaling trend

Using FDTD simulation tool, the plasmon resonance and near-field couplings between three identical nanocubes made of gold material arranged in face-to-face configuration are investigated at a diverse range of transverse shifts and a constant gap separation. The dipole–dipole coupling approximation fails to explain the coupling features when the shift is smaller than the cube's size and this due to the excitation of higher-order modes as the polarization pattern switched from facing facets into facing edges. The results of the simulations show the resonance wavelength is unexpectedly redshifted and contradicts the expected blue shift by the dipole–dipole model.