Plasmons dispersion and nonvertical interband transitions in single crystal Bi2Se3 investigated by electron energy-loss spectroscopy

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 (similar to 5.5 and 10 eV) were demonstrated in STEM-EELS spectra and the corresponding spectral imaging in real space. In 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 exhibited 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. DOI: 10.1103/PhysRevB.87.085126