Kohn Anomalies and Electron-Phonon Interactions in Graphite

Kohn Anomalies in Graphite and Nanotubes

Atomic vibrations are partially screened by electrons. In a metal this screening can change rapidly for vibrations associated to certain points of the Brillouin zone, entirely determined by the shape of the Fermi surface. The consequent anomalous behaviour of the phonon dispersion is called Kohn anomaly. Graphite is a semimetal. Nanotubes can be metals or semiconductors. We demonstrate that two...

Phonon linewidths and electron-phonon coupling in graphite and nanotubes

We show that electron-phonon coupling EPC is the major source of broadening for the Raman G and G− peaks in graphite and metallic nanotubes. This allows us to directly measure the optical-phonon EPCs from the G and G− linewidths. The experimental EPCs compare extremely well with those from the density functional theory. We show that the EPC explains the difference in the Raman spectra of metall...

Electron-phonon interactions and superconductivity.

Kohn anomalies in superconductors.

I present the detailed behavior of phonon dispersion curves near momenta which span the electronic Fermi sea in a superconductor. I demonstrate that an anomaly, similar to the metallic Kohn anomaly, exists in a superconductor’s dispersion curves when the frequency of the phonon spanning the Fermi sea exceeds twice the superconducting energy gap. This anomaly occurs at approximately the same mom...

Electron–phonon interaction and relaxation time in graphite

The electron–phonon (e–ph) interaction and the relaxation time of photo-excited electrons are calculated in graphite within the tight-binding scheme. The e–ph matrix element thus obtained, shows anisotropy in k-space. The calculated relaxation time is of the same order of magnitude as the experimental one. Moreover, below an energy close to the Fermi energy, the absorption rate exceeds the emis...