Metallic nanoantennas have been studied as efficient coherent phonon generators and detectors, harnessing their characteristic optical absorption and polarization dependence of the optical modes [1-2]. The ability to control the excitation of phononic modes depends on the properties of the multiple optical resonances of the system. Lately, it has been made possible to optimally excite and detect phonon modes via plasmon resonances at the same optical frequency using chiral nanostructures and circularly polarized light [3]. However, torsional modes remain elusive in nanophononic studies. We have pursued two different approaches, one consisting in a twisted single nanostructure (toroidal propeller) [4] the second being composed of two coupled bars [5]. The twisting of the phononic mode is provided by the peculiar geometry of the nano-nanoantenna, either intrinsic in the case of the toroidal propeller or as a result of the interaction of the bars though the substrate.
In this work, we will present a complete theoretical analysis of the phononic and plasmonic modes, as well as their surface deformation field profiles in the two-coupled-bars system.
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