9 research outputs found
Neutral triplet Collective Mode as a new decay channel in Graphite
In an earlier work we predicted the existence of a neutral triplet collective
mode in undoped graphene and graphite [Phys. Rev. Lett. {\bf 89} (2002) 16402].
In this work we study a phenomenological Hamiltonian describing the interaction
of tight-binding electrons on honeycomb lattice with such a dispersive neutral
triplet boson. Our Hamiltonian is a generalization of the Holstein polaron
problem to the case of triplet bosons with non-trivial dispersion all over the
Brillouin zone. This collective mode constitutes an important excitation branch
which can contribute to the decay rate of the electronic excitations. The
presence of such collective mode, modifies the spectral properties of electrons
in graphite and undoped graphene. In particular such collective mode, as will
be shown in this paper, can account for some part of the missing decay rate in
a time-domain measurement done on graphite
Short range Coulomb correlations render massive Dirac fermions massless
Tight binding electrons on a honeycomb lattice are described by an effective
Dirac theory at low energies. Lowering symmetry by an alternate ionic potential
() generates a single-particle gap in the spectrum. We employ the
dynamical mean field theory (DMFT) technique, to study the effect of on-site
electron correlation () on massive Dirac fermions. For a fixed mass
parameter , we find that beyond a critical value
massive Dirac fermions become massless. Further increasing beyond
, there will be another phase transition to the Mott insulating
state. Therefore the competition between the single-particle gap parameter,
, and the Hubbard restores the semi-metallic nature of the parent
Hamiltonian. The width of the intermediate semi-metallic regime shrinks by
increasing the ionic potential. However, at small values of , there is
a wide interval of values for which the system remains semi-metal.Comment: 4 pages, 5 figure
Ultrafast electron-optical phonon scattering and quasiparticle lifetime in CVD-grown graphene
10.1021/nn200419zACS Nano543278-328