Direct observation of the electron-phonon coupling between empty states in graphite via high-resolution electron energy-loss spectroscopy

Electron-phonon coupling (EPC) in graphite was investigated via high-resolution electron energy-loss spectroscopy and first-principles band calculations. We found strong resonance enhancements in the magnitude of specific phonon scatterings at specific primary energies of the incident electron. This result is attributed to a new scattering mechanism, where the incident electron is trapped at an unoccupied band, is scattered into another band via EPC with a specific phonon, and is finally detected by the analyzer. The scattering intensity is related to the electron-phonon matrix element wherein the energy and momenta of both electron and phonon are resolved.