Photonic and phononic modes in acoustoplasmonic toroidal nanopropellers

TL;DR

This paper investigates unique acoustic and photonic resonances in toroidal nanopropellers, revealing how their spectral properties depend on geometric parameters and demonstrating significant helicity-dependent optical absorption.

Contribution

It introduces a novel understanding of resonances in toroidal nanopropellers, linking geometry with spectral shifts and resonance modes for both optical and acoustic responses.

Findings

Spectral resonances shift to lower frequencies as the spiral angle increases.

Optical resonances exhibit a helicity-dependent absorption cross section.

New low-frequency acoustic resonances appear with small spiral angles.

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.