Disentangling multipole contributions to collective excitations in fullerenes

TL;DR

This paper uses ab initio calculations and non-negative matrix factorization to analyze multipole contributions to collective excitations in C60 fullerenes, proposing a new experimental approach with electron vortex beams.

Contribution

It introduces a method to isolate and visualize multipole contributions in collective excitations of fullerenes, combining ab initio calculations with analytical modeling.

Findings

Excellent agreement between model, ab initio calculations, and experimental data

Identification of multipole contributions in collective modes

Proposal of using electron vortex beams for selective excitation

Abstract

Angular resolved electron energy-loss spectroscopy (EELS) gives access to the momentum and the energy dispersion of electronic excitations and allows to explore the transition from individual to collective excitations. Dimensionality and geometry play thereby a key role. As a prototypical example we analyze theoretically the case of Buckminster fullerene C60 using ab initio calculations based on the time-dependent density-functional theory. Utilizing the non-negative matrix factorization method, multipole contributions to various collective modes are isolated, imaged in real space, and their energy and momentum dependencies are traced. A possible experiment is suggested to access the multipolar excitations selectively via EELS with electron vortex (twisted) beams. Furthermore, we construct an accurate analytical model for the response function. Both the model and the ab initio cross sections are in excellent agreement with recent experimental data.