Аннотация
The interaction of monolayer graphene with specific substrates may break
its sublattice symmetry and results in unidirectional chiral states with
opposite group velocities in the different Dirac cones (Zarenia et al
2012 Phys. Rev. B 86 085451). Taking advantage of this feature, we
propose a valley filter based on a transversal mass kink for low energy
electrons in graphene, which is obtained by assuming a defect region in
the substrate that provides a change in the sign of the
substrate-induced mass and thus creates a non-biased channel,
perpendicular to the kink, for electron motion. By solving the
time-dependent Schrodinger equation for the tight-binding Hamiltonian,
we investigate the time evolution of a Gaussian wave packet propagating
through such a system and obtain the transport properties of this
graphene-based substrate-induced quantum point contact. Our results
demonstrate that efficient valley filtering can be obtained, provided:
(i) the electron energy is sufficiently low, i.e. with electrons
belonging mostly to the lowest sub-band of the channel, and (ii) the
channel length (width) is sufficiently long (narrow). Moreover, even
though the transmission probabilities for each valley are significantly
affected by impurities and defects in the channel region, the valley
polarization in this system is shown to be robust against their
presence.
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