Photonic and phononic modes in acoustoplasmonic toroidal nanopropellers

Abstract

Non-conventional resonances, both acoustic and photonic, are found in metallic particles with a toroidal nanopropeller geometry that is generated by sweeping a three-lobed 2D-shape along a spiral with twisting angle, $\alpha$. For both optical and acoustic cases, spectral location of resonances experiences a red-shift as a function of $\alpha$. We demonstrate that the optical case can be understood as a natural evolution of resonances as the spiral length of the toroidal nanopropeller increases with $\alpha$, implying a huge helicity dependent absorption cross section. In the case of acoustic response, two red-shifting breathing modes are identified. Additionally, even small $\alpha$ allows the appearance of new low-frequency resonances, whose spectral dispersion depends on a competition between length of the generative spiral and the pitch of the toroidal nanopropeller.

9 pages 7 figures