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

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’'.

💡 Research Summary

The paper presents a comprehensive study of collective electronic dipole excitations in C₆₀ fullerenes using the Local Current Approximation (LCA), a semiclassical method derived from a variational principle. After a brief historical overview of the two classic models for the nuclear giant dipole resonance—the translational Goldhaber‑Teller mode and the compressional Steinwedel‑Jensen‑Migdal mode—the authors introduce the LCA framework. Starting from the many‑body Schrödinger equation, they define the first‑ and third‑order energy moments (m₁ and m₃) and formulate a variational condition δE₃