Revealing the quantum regime in tunnelling plasmonics

Area of Science:

• Physics
• Materials Science
• Nanotechnology

Background:

• Optically driven free electrons in metal nanostructures couple electrically across nanometre gaps, forming plasmons with confined optical fields.
• Plasmonic coupling is crucial for nanophotonic technologies like sensors, active devices, and photovoltaics.
• Classical treatments fail at subnanometre gaps where quantum tunnelling and extreme non-locality emerge.

Purpose of the Study:

• To investigate the quantum regime of tunnelling plasmonics at subnanometre separations.
• To provide a new description of non-local transport driven by quantum tunnelling across nanogaps.
• To experimentally validate quantum-based models for plasmonic systems.

Main Methods:

• Simultaneously measuring electrical and optical properties of gold nanostructures with controllable subnanometre separation.
• Comparing experimental results with quantum-based theoretical models.

Main Results:

• Observed phenomena in tunnelling plasmonics agreed well with quantum-based models.
• Quantum tunnelling eliminated classical theory singularities.
• A quantum limit for plasmonic field confinement of approximately 10(-8)λ(3) for visible light was established.

Conclusions:

• Tunnelling plasmonics operate in a quantum regime distinct from classical descriptions.
• Quantum tunnelling dictates the ultimate limit of plasmonic field confinement.
• Findings will influence future nanoplasmonic device engineering and nanoscale photochemistry research.