Kohn anomalies and electron-phonon interactions in graphite

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, while they are negligible for all the other modes at Gamma and K.