Plasmon Coupling-Induced Suppression of Optical Anisotropy in Offset Gold Nanorod Heterodimer

The drastically suppressed polarization anisotropy in the overlapping region of offset gold nanorod (AuNR) heterodimers, a key challenge in polarization-robust nanophotonics, arises from gap-plasmon-mediated energy delocalization. Here, we investigate an offset AuNR heterodimer with controlled size mismatch and sub-15 nm gap, using scanning polarization modulation microscopy (SPMM), scanning electron microscopy (SEM), and finite-difference time-domain (FDTD) simulations. The heterodimer exhibits a significant suppression (>60%) of polarization-dependent differential transmission (ΔT) in the overlapping site, compared to single AuNRs. This anisotropic suppression originates from gap-plasmon-mediated energy homogenization, where multipolar interactions redistribute electromagnetic energy across orthogonal polarizations. Jones matrix analysis reveals a sinusoidal dependence of ΔT on incident polarization angles, while FDTD simulations confirm polarization-insensitive electric field enhancement (|E/E₀|>6) localized within the inter-rod gap. These results highlight a geometry-driven mechanism for suppressed polarization-dependent plasmon response, providing design principles for designing tunable nanophotonic devices with tailored anisotropy.