New coupling mechanism and plasmonic scaling trend in transversely shifted cubic homodimers

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Alsawafta, Mohammed
Journal Article
The impact of transition between facing facets and facing edges polarization states on the spectral response of cubic homodimers made of Ag and Au is comprehensively investigated by employing the finite-difference time-domain (FDTD) numerical tool. The transition is achieved by shifting one of the two resonators in a perpendicular direction to the interparticle axis. From the simulation results and analytical treatment of the collected data, as the value of transverse shift (h) alters, it is observed that the universal scaling behavior cannot be used to predict either the amount or type of the plasmon shift in the excited coupled modes. For both homodimers, depending on the relative value of h and the cube’s width (w), the fractional plasmon shift exhibits both a redshift and blueshift. As h increases, the resonance wavelength of the excited mode redshifts when h ≤ 0.8 w, and then, it is followed by a blueshift once h exceeds 0.8 w. The mathematical formalism of each shift as a function of h is well-described by the sigmoidal (S-curve) functions. This demonstrates that the previously proposed universal scaling trend in homodimers cannot be fully employed to study the distance-dependent plasmon resonance in non-aligned homodimers. The dependency of the nearfield enhancement factor on h has been investigated as well via fractional field factor shift. It is found that for roughly the same fitting region, both Ag and Au exhibit different scaling behaviors due to the difference in the excitation energy and corresponding intensity of the higher order modes.