Schüler M., Berakdar J., Pavlyukh Y.

Angular resolved electron energy-loss spectroscopy (EELS) gives access to the momentum and the energy dispersion of electronic excitations and allows one to explore the transition from individual to collective excitations. Dimensionality and geometry thereby play a key role. As a prototypical example we theoretically analyze 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 good agreement with recent experimental data.

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