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

TL;DR

This study investigates plasmons and interband transitions in Bi2Se3 single crystals using electron energy-loss spectroscopy, revealing distinct dispersion behaviors and identifying nonvertical interband transitions.

Contribution

The paper provides detailed experimental analysis of plasmons and interband transitions in Bi2Se3, highlighting unique dispersion behaviors and identifying nonvertical interband transitions for the first time.

Findings

Volume and surface plasmons identified in spectra.

{}+{} plasmons show quadratic dispersion.

{} plasmon exhibits linear dispersion similar to graphene.

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 ({\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.