Kohn Anomalies and Electron-Phonon Interaction in Graphite

TL;DR

This paper investigates the phonon dispersion in graphite, identifying two Kohn anomalies at specific modes, and establishes a direct relation between the anomalies' features and the electron-phonon coupling strength, enabling experimental measurement.

Contribution

It provides an exact analytic derivation linking phonon dispersion anomalies to electron-phonon coupling in graphite, highlighting the modes with significant EPC.

Findings

Identified two Kohn anomalies at Gamma and K points.

Derived that kink slopes are proportional to EPC squared.

Found large EPC at specific phonon modes.

Abstract

We demonstrate that graphite phonon dispersions have two Kohn anomalies at the Gamma-E_2g and K-A'1 modes. The anomalies are revealed by two sharp kinks. By an exact analytic derivation, we show that the slope of these kinks is proportional to the square of the electron-phonon coupling (EPC). Thus, we can directly measure the EPC from the experimental dispersions. The Gamma-E_2g and K-A'1 EPCs are particularly large, whilst they are negligible for all the other modes at Gamma and K.