S. C. Liou, M. -W. Chu, R. Sankar, F. -T. Huang, G. -J. Shu, F. C. Chou, C. H. Chen
Plasmons dispersion and nonvertical interband transitions in Bi2Se3 single crystals were investigated by electron energy-loss spectroscopy in conjunction with (scanning) transmission electron microscopy, (S)TEM-EELS. Both volume plasmons ({\pi} plasmon at 7 eV and {\pi}+{\sigma} plasmon at 17 eV) and surface plasmons (~5.5 and 10 eV) were demonstrated in STEM-EELS spectra and the corresponding spectral imaging in real space. In the further EELS experiments in reciprocal space, the momentum-dependent spectra reveal very different dispersion behavior between {\pi} and {\pi}+{\sigma} plasmons, with {\pi}+{\sigma} plasmons showing a typical quadratic dependence whereas the {\pi} plasmon exhibiting a linear dispersion analogous to what was reported for graphene. Furthermore, a low energy excitation 0.7~1.6 eV was also observed which is attributed to direct nonvertical interband transitions along the gamma-F direction.
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http://arxiv.org/abs/1301.0378
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