radius 20 nm, length 100 nm, and gap distance 20 nm.[]{data-label="fig:PDB"}](Fig_PDB.png)

Hybridized plasmonic structures can exhibit higher-order multipole modes even with subwavelength feature sizes [@Arango2014; @Fruhnert2017]. Among them, plasmonic double bars (PDB) has exhibited strong MD mode even at the visible regime [@Dolling2005]. Multipole-decomposed scattering cross-section exhibits broad ED resonance at 490 nm and sharp EQ and MD resonances at 530 nm (Fig. \[fig:PDB\]c), and the origins of the multipolar modes can be analyzed from retrieved $\boldsymbol{\alpha}$-tensor (Fig. \[fig:PDB\]b) and spectra of its components (Fig. \[fig:PDB\]d). The broad ED resonance is easily attributed to $(\alpha_{e1}^{e1})_{x}^{x}$, and the sharp EQ and MD resonances are spectrally attributed to $(\alpha_{m1}^{m1})_{z}^{z}$, $(\alpha_{e2}^{e2})_{xy}^{xy}$, and $(\alpha_{e2}^{m1})_{xy}^{z}$. Analysis from $\boldsymbol{\alpha}$-tensor allows us to see that PDB has different origin of optical magnetism from split-ring resonators [@Arango2013; @Liu2016] and high-refractive-index spheres (see Appendix \[appendix:t-matrix\] for more details). Importantly, only a few components are dominant in the retrieved $\boldsymbol{\alpha}$-tensor, making the analysis easier (Fig. \[fig:PDB\]b). This simplification partly comes from the particle symmetry. Notably, the parity symmetry removes the half of the components: $\alpha_{e1}^{e2}$, $\alpha_{e2}^{e1}$, $\alpha_{e1}^{m1}$, $\alpha_{m1}^{e1}$, $\alpha_{e2}^{m2}$, $\alpha_{m2}^{e2}$, $\alpha_{m1}^{m2}$, and $\alpha_{m2}^{m1}$. Strong anisotropicity of the meta-atom further simplifies the $\boldsymbol{\alpha}$-tensor, especially in the Cartesian basis. In addition, the 