Floquet Spectrum and Transport Through an Irradiated Graphene Ribbon. (arXiv:1106.0302v1 [cond-mat.mes-hall])

Graphene subject to a spatially uniform, circularly-polarized electric field
supports a Floquet spectrum with properties akin to those of a topological
insulator, including non-vanishing Chern numbers associated with bulk bands and
current-carrying edge states. Transport properties of this system however are
complicated by the non-equilibrium occupations of the Floquet states. We
address this by considering transport in a two-terminal ribbon geometry for
which the leads have well-defined chemical potentials, with an irradiated
central scattering region. We demonstrate the presence of edge states, which
for infinite mass boundary conditions may be associated with only one of the
two valleys. At low frequencies, the bulk DC conductivity near zero energy is
shown to be dominated by a series of states with very narrow anticrossings,
leading to super-diffusive behavior. For very long ribbons, a ballistic regime
emerges in which edge state transport dominates.

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