Coulomb effects on the photo-excited quantum dynamics of electrons in a plasmonic nanosphere

TL;DR

This paper investigates how Coulomb interactions influence the quantum dynamics of electrons in small plasmonic nanospheres, combining quantum and collective effects to better understand nonlinear optical responses.

Contribution

It provides a microscopic density matrix analysis of Coulomb effects on photo-excited electron dynamics in nanospheres, highlighting collective and nonlinear phenomena.

Findings

Discrete resonances from Coulomb-mediated collective response

Oscillations between interacting eigenstates in nonlinear regime

Insights into quantum and nonlinear plasmonic behavior

Abstract

With recent experiments investigating the optical properties of progressively smaller plasmonic particles, quantum effects become increasingly more relevant, requiring a microscopic description. Using the density matrix formalism we analyze the photo-excited few-electron dynamics of a small nanosphere. Following the standard derivation of the bulk plasmon we particularly aim on elucidating the role of the Coulomb interaction. Calculating the dielectric susceptibility spectrum in the linear optical response we find discrete resonances resulting from a collective response mediated by the Coulomb interaction between the electrons. In the nonlinear regime, the occupations of the system exhibit oscillations between the interacting eigenstates. Our approach provides an ideal platform to study and explain nonlinear and quantum plasmonics, revealing that the photo-excited dynamics of plasmonic nano spheres has similarities with and combines characteristics of both, the well-known two-level Rabi dynamics, and the collective many-electron behavior typical of plasmons.