Beyond the Quantum Picture: The Electrodynamic Origin of Chiral Nanoplasmonics

Abstract

Chiral plasmonic nanostructures are rapidly emerging as ideal substrates for enantioselective sensing, chiral near-field engineering, and plasmon-assisted catalysis, owing to their exceptional sensitivity to structural handedness. However, the physical origin of plasmonic chirality, whether intrinsically quantum or primarily governed by collective electrodynamics, remains an open question, limiting the development of predictive theoretical methods for the design of novel chiral plasmonic architectures. Here, we show that a fully atomistic classical electrodynamic model, coupling intraband charge transport and interband polarization, quantitatively reproduces state-of-the-art \textit{ab initio} and experimental chiroptical spectra across the quantum-to-classical regime, from atomistically defined chiral Ag and Au nanostructures to DNA-origami-assembled Au nanorods containing up to $\sim 10^5$ atoms. Our results support a unified electrodynamic origin of plasmonic chirality, providing the missing foundation to connect local structural motifs to chiroptical response and local chiral near fields, and paving the way for the atomistically defined, rational design of chiral plasmonic nanostructures optimized for targeted applications.

Figures (4)

• Figure 1: (a) Examples of the Ag:DNA structures in trimer arrangements, adapted from ref schultz2013evidence. (b-c) structures and calculated CD spectra of Ag nanochains as a function of the number of atoms. Reference TDDFT spectra are recovered from Ref. karimova2015time, performed at the SAOP/TZP levels by including relativistic effects via ZORA corrections. (d) $\omega$FQF$\mu$ imaginary part of induced densities for Ag$_{12}$ at the three main plasmon resonances for the specified field polarizations.
• Figure 2: (a) Side and top view of 1R--3R gold helices structures. (b) $\omega$FQF$\mu$ (left) and TDDFT (right) CD spectra decomposed in Cartesian components. TDDFT results are recovered from Ref. toffoli2021circularly, and were computed at the polTDDFT/LB94/TZP level, by including relativistic correction via ZORA. (c) $\omega$FQF$\mu$ imaginary densities (isovalue 0.01 a.u.) computed at the two main plasmon resonances of 2R ($\omega=0.96$ and 1.60 eV) induced by $x$ and $y$-polarized electric field.
• Figure 3: (a) Side and top view of parallel (top) and tilted gold assembled nanotubes. (b) $\omega$FQF$\mu$ (top) and TDDFT (bottom) absorption (left) and CD (right) spectra of assembled nanotubes as a function of the tilting angle. TDDFT results are recovered from Ref. toffoli2021plasmonic, and were computed at the polTDDFT/LB94/TZP level, by including relativistic corrections via ZORA. The Cartesian decomposition of the absorption and CD signals for $\alpha = 45^{\circ}$ is given as insets.
• Figure 4: Structures (a) and $\omega$FQF$\mu$ CD spectra (b) of chiral DNA-origami-templated gold nanorod assemblies in dimer (left), trimer (middle), and tetramer (right) configurations. The experimental spectra from Ref. wang2019reconfigurable are given as insets.