Breaking the morphological and compositional symmetries of metallic nanoparticle (NP) dimers provides a novel approach to modulate plasmon coupling between the NPs. In this study, we theoretically investigate the effect of symmetry breaking on the plasmonic coupling in morphologically asymmetric Au nanoring-nanodisk (NR-ND) dimer, compositionally heterogeneous Au-Ag nanoring dimer, and compositionally as well as morphologically asymmetric Au-Ag NR-ND heterodimers. It has been found that when the inner radii of symmetrical Au NR dimer is decreased, the scattering spectral intensity of coupled bonding mode and higher-order coupled bonding mode drastically decreases and increases, respectively. Besides, the effect of aspect ratio on the plasmon resonance modes is investigated. Furthermore, with fixed geometric parameters of one NR and by morphing the shape of the other NR into ND through inner radius, we show the generation and modification of a Fano resonance. As a result of introducing morphological and compositional asymmetry separately, single Fano-type spectral feature is observed in the scattering spectra. We demonstrate that the double Fano resonances can be easily achieved in compositionally and morphologically asymmetric heterodimer with double symmetry breaking. These dual modes are caused by the interference of dipolar bright mode (localized LSPR modes) of Ag NP with the quadrupole and hexapole modes (interband transitions) of the Au NP. Finally, at optimum asymmetric heterodimers, we discussed the effect of refractive index on the Fano-type resonance. These new and simple designs provide a novel insight to modulate optical response and the generation of higher-order Fano resonances, which have many potential applications such as in photonics and refractive index sensing.

打破金属纳米粒子（NP）二聚体的形态和组成对称性提供了一种新颖的方法来调节NP之间的等离激元耦合。在这项研究中，我们从理论上研究了对称断裂对形态不对称的金纳米环-纳米圆盘（NR-ND）二聚体，组成异质的Au-Ag纳米环二聚体，以及组成和形态不对称的Au-Ag NR-的等离激元耦合的影响。 ND异二聚体。已经发现，当对称的Au NR二聚体的内半径减小时，耦合键合模式和高阶耦合键合模式的散射光谱强度分别急剧减小和增大。此外，研究了纵横比对等离子体共振模式的影响。此外，在一个NR的几何参数固定的情况下，通过将另一个NR的形状通过内半径变形为ND，我们展示了Fano共振的产生和修改。由于分别引入了形态和组成不对称性，在散射光谱中观察到了单个Fano型光谱特征。我们证明，可以在具有双对称断裂的组成和形态上不对称异二聚体中容易地实现双Fano共振。这些双重模式是由Ag NP的偶极亮模式（局部LSPR模式）与Au NP的四极和六极模式（带间跃迁）的干扰引起的。最后，在最佳不对称异二聚体上，我们讨论了折射率对Fano型共振的影响。