Kohn Anomalies and Electron-Phonon Interactions in Graphite

We demonstrate that graphite phonon dispersions have two Kohn anomalies at the $\Gamma \mathrm{\text{−}}{E}_{2g}$ and $\mathbf{K}\mathrm{\text{−}}{A}_1^{\prime }$ 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 $\Gamma \mathrm{\text{−}}{E}_{2g}$ and $\mathbf{K}\mathrm{\text{−}}{A}_1^{\prime }$ EPCs are particularly large, while they are negligible for all the other modes at $\Gamma$ and $\mathbf{K}$.