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

Abstract

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 (π plasmon at 7 eV and π+σ 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 π and π+σ plasmons, with π+σ plasmons showing a typical quadratic dependence whereas the π 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.