Seminars Archive

Electron-phonon interaction in graphene:non-adiabatic Kohn anomalies and electron-mass enhancement.

Abstract
We use density functional theory calculations and analytical results, to study the renormalization of phonon and electron properties due to the electron-phonon interaction. Our description of the phonon properties closely reproduces the experimental data. In particular, the peculiar Dirac-like band structure of graphite, induces Kohn anomalies both in the phonon dispersion [1] and in the dependence of the phonon frequency and lifetime on doping [2,3]. Interestingly, the accurate description of such anomalies requires the inclusion of effects beyond the adiabatic approximation. On the contrary, our calculations do not reproduce the electron properties as measured by ARPES [4]. The electron-phonon coupling extracted from the kink observed in ARPES experiments is roughly a factor of 5.5 larger than the calculated one. This disagreement is partially reconciled by the inclusion of resolution effects. Indeed we show that a finite resolution increases the apparent electron-phonon coupling and the discrepancy between theory and experiments is thus reduced to a factor of 2. From the linewidth of the calculated ARPES spectra we obtain the electron relaxation time. A comparison with available experimental data in graphene shows that the electron relaxation time detected in ARPES is almost two orders of magnitudes smaller than what measured by other experimental techniques. [1] S. Piscanec, M. Lazzeri, F. Mauri, A. C. Ferrari, and J. Robertson Phys. Rev. Lett. 93, 185503 (2004) [2] M. Lazzeri, F. Mauri, Phys. Rev. Lett. 97, 266407 (2006) [3] S. Pisana, M. Lazzeri, C. Casiraghi, K.S. Novoselov, A.K.Geim, A.C. Ferrari, F. Mauri, Nature Materials 6, 198-201 (2007) [4] M Calandra, F. Mauri, Phys. Rev. B, to be published (preprint arXiv:0707.1467)