Seminars Archive
Electron-phonon interaction in graphene:non-adiabatic Kohn anomalies and electron-mass enhancement.
Institut de Minéralogie et de Physique des Milieux Condensés,Université Pierre et Marie Curie,Paris
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)