How To Identify Plasmons from the Optical Response of Nanostructures

Area of Science:

• Plasmonics and Nanophotonics
• Quantum Mechanics and Condensed Matter Physics

Background:

• Plasmonics traditionally relies on classical electromagnetic theory for larger structures.
• Quantum mechanical effects become dominant in nanostructures below a few nanometers.
• Distinguishing collective plasmonic modes from single-electron excitations is challenging at the nanoscale.

Purpose of the Study:

• To develop a universal metric for classifying optical resonances in ultrasmall nanostructures.
• To rigorously differentiate plasmonic behavior from nonplasmonic excitations.
• To provide a foundation for designing and understanding molecular plasmonics.

Main Methods:

• Utilized rigorous quantum mechanical computational techniques.
• Defined and implemented a generalized plasmonicity index (GPI).
• Applied the GPI to various physical systems, including jellium spheres, metallic clusters, and nanostructured graphene.

Main Results:

• The generalized plasmonicity index (GPI) successfully classifies optical resonances as plasmonic or nonplasmonic.
• Demonstrated the emergence of plasmonic behavior with increasing size and electron count in jellium spheres.
• Characterized plasmonicity in atomic-scale clusters and nanostructured graphene, down to molecular plasmons.

Conclusions:

• The GPI offers a universal and computationally accessible method for identifying plasmons.
• Quantum effects significantly alter plasmonic responses in ultrasmall nanostructures.
• This work establishes a rigorous framework for advancing molecular plasmonics and ultrasmall nanostructure design.