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Large-scale tight-binding simulations of quantum transport in ballistic graphene.
Calogero G(1), Papior NR(2), Boggild P(3), Brandbyge M(4).
(1)Danmarks Tekniske Universitet Nanotek, Lyngby, 2800, DENMARK.
(2)Nanotech, The Danish Technical University, Ørsteds Plads, building 345E, 2800,
Kgs. Lyngby, Kgs. Lyngby, 2800, DENMARK.
(3)DTU Nanotech, Technical University of Denmark, Ørsteds Plads, Building 345
east, Kgs. Lyngby, 2800, DENMARK.
(4)Dept. of micro and nanotechnology, Technical University of Denmark, Building
345 East, DK-2800 Lyngby, Kongens Lyngby, DK-2800, DENMARK.
Graphene has proven to host outstanding mesoscopic effects involving massless
Dirac quasiparticles travelling ballistically resulting in the current flow
exhibiting light-like behaviour. A new branch of 2D electronics inspired by the
standard principles of optics is rapidly evolving, calling for a deeper
understanding of transport in large-scale devices at a quantum level. Here we
perform large-scale quantum transport calculations based on a tight-binding model
of graphene and the non-equilibrium Green’s function method and include the
effects of <i>p-n</i> junctions of different shape, magnetic field,
and absorptive regions acting as drains for current. We stress the importance of
choosing absorbing boundary conditions in the calculations to correctly capture
how current flows in the limit of infinite devices. As a specific application we
present a fully quantum-mechanical framework for the « 2D Dirac fermion
microscope » recently proposed by Bøggild <i>et al.</i>
[<i>Nature Comm.</i> <b>8</b>, 10.1038 (2017)], tackling
several key electron-optical effects therein predicted via semi-classical trajectory simulations, such as electron beam collimation, deflection and
scattering off Veselago dots. Our results confirm that a semiclassical approach
to a large extent is sufficient to capture the main transport features in the
mesoscopic limit and the optical regime, but also that a richer electron-optical
landscape is to be expected when coherence or other purely quantum effects are
accounted for in the simulations.
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