Coupling of Surface and Volume Dipole Oscillations in C-60 Molecules

TL;DR

This paper reviews the local-current approximation (LCA) for collective excitations in finite fermion systems, applies it to C60 molecules, and compares its predictions with microscopic calculations and experiments, highlighting the coupling of surface and volume plasmons.

Contribution

It introduces and applies the LCA to model coupled surface and volume dipole oscillations in C60 molecules, showing semi-quantitative agreement with detailed TDLDA calculations.

Findings

LCA captures coupling of surface and volume plasmons in C60.

Semi-quantitative agreement between LCA and TDLDA calculations.

Experimental observations of volume plasmons are qualitatively supported.

Abstract

We first give a short review of the ``local-current approximation'' (LCA), derived from a general variation principle, which serves as a semiclassical description of strongly collective excitations in finite fermion systems starting from their quantum-mechanical mean-field ground state. We illustrate it for the example of coupled translational and compressional dipole excitations in metal clusters. We then discuss collective electronic dipole excitations in C$_{60}$ molecules (Buckminster fullerenes). We show that the coupling of the pure translational mode (``surface plasmon'') with compressional volume modes in the semiclasscial LCA yields semi-quantitative agreement with microscopic time-dependent density functional (TDLDA) calculations, while both theories yield qualitative agreement with the recent experimental observation of a ``volume plasmon''.