Atomic-Scale Lightning Rod Effect in Plasmonic Picocavities: A Classical View to a Quantum Effect.

Area of Science:

• Quantum nanophotonics
• Plasmonics
• Surface-enhanced spectroscopy

Background:

• Plasmonic gaps concentrate optical fields to nanoscale volumes (hundreds of nm³).
• Atomic-scale features at gap interfaces can further influence these fields.

Purpose of the Study:

• To investigate subnanometric electromagnetic field localization at atomic-scale features in plasmonic gaps.
• To compare quantum calculations with classical models for describing these extreme optical cavities.

Main Methods:

• Atomistic quantum calculations using time-dependent density functional theory (TDDFT).
• Classical modeling of the lightning rod effect at the atomic scale.
• Comparison of near-field distributions from quantum and classical approaches.

Main Results:

• Atomic features induce subnanometric localization and enhancement of optical fields, beyond the plasmonic background.
• This effect is robust against dynamical screening and spill-out.
• A classical model accurately describes the atomic-scale lightning rod effect and validates classical methods for calculating effective mode volumes.

Conclusions:

• Atomic-scale features create significant electromagnetic field enhancements in plasmonic gaps.
• Classical models are sufficient for describing these extreme subnanometric optical cavities.
• Findings are vital for surface-enhanced molecular spectroscopy and quantum nanophotonics.