Plasmonic breathing modes in $\rm C_{60}$ molecules -- A quantum hydrodynamic approach

TL;DR

This paper introduces a quantum hydrodynamic model to describe plasmonic breathing modes in C60 molecules, capturing key quantum effects with simpler computations than TDDFT, and confirms the existence of multiple collective modes.

Contribution

The paper develops a simplified quantum hydrodynamic approach to analyze plasmonic oscillations in C60, including key quantum effects, and validates it against TDDFT results.

Findings

Identification of a bulk plasmonic mode near the plasmon frequency.

Discovery of a second lower-energy collective mode.

Confirmation of modes via numerical simulations and potential experimental detection.

Abstract

We propose and illustrate a quantum hydrodynamic (QHD) model for the description of plasmonic oscillations in the $\rm C_{60}$ molecule. Although simpler than competing approaches such as time-dependent density functional theory (TDDFT), the model contains the key ingredients to characterize plasmonic modes, namely the Hartree, exchange and correlation potentials, as well as nonlocal, nonlinear and quantum effects to the lowest order. A variational technique is used to solve analytically the QHD model for the case of breathing (monopolar) plasmonic oscillations, revealing a bulk mode near the plasmon frequency. Numerical simulations of both the QHD equations and a TDDFT model confirm the existence of this mode and highlight a second collective mode at lower energy. Such monopolar modes may be measured experimentally using electron energy loss spectroscopy.