Kohn Anomalies and Electron-Phonon Interactions in Graphite

We demonstrate that graphite phonon dispersions have two Kohn anomalies at the Γ-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 Γ-E_2g and K-A'₁ EPCs are particularly large, while they are negligible for all the other modes at Γ and K.