334 research outputs found
One-dimensional topological channels in heterostrained bilayer graphene
The domain walls between AB- and BA-stacked gapped bilayer graphene have
garnered intense interest as they host topologically-protected,
valley-polarised transport channels. The introduction of a twist angle between
the bilayers and the associated formation of a Moire pattern has been the
dominant method used to study these topological channels, but heterostrain can
also give rise to similar stacking domains and interfaces. Here, we
theoretically study the electronic structure of a uniaxially heterostrained
bilayer graphene. We discuss the formation and evolution of interface-localized
channels in the one-dimensional Moire pattern that emerges due to the different
stacking registries between the two layers. We find that a uniform heterostrain
is not sufficient to create one-dimensional topological channels in biased
bilayer graphene. Instead, using a simple model to account for the in-plane
atomic reconstruction driven by the changing stacking registry, we show that
the resulting expanded Bernal-stacked domains and sharper interfaces are
required for robust topological interfaces to emerge. These states are highly
localised in the AA- or SP-stacked interface regions and exhibit differences in
their layer and sublattice distribution depending on the interface stacking. We
conclude that heterostrain can be used as a mechanism to tune the presence and
distribution of topological channels in gapped bilayer graphene systems,
complementary to the field of twistronics.Comment: 10 pages, 7 figure
Energy gap tuning in graphene on hexagonal boron nitride bilayer system
We use a tight binding approach and density functional theory calculations to
study the band structure of graphene/hexagonal boron nitride bilayer system in
the most stable configuration. We show that an electric field applied in the
direction perpendicular to the layers significantly modifies the electronic
structure of the whole system, including shifts, anticrossing and other
deformations of bands, which can allow to control the value of the energy gap.
It is shown that band structure of biased system may be tailored for specific
requirements of nanoelectronics applications. The carriers' mobilities are
expected to be higher than in the bilayer graphene devices.Comment: 10 pages, 7 figures, submitted to Physical Review
Study of edge states and conductivity in spin-orbit coupled bilayer graphene
We present an elaborate and systematic study of the conductance properties of
a zigzag bilayer graphene nanoribbon modeled by a Kane-Mele (KM) Hamiltonian.
The interplay of the Rashba and the intrinsic spin-orbit couplings with the
edge states, electronic band structures, charge and spin transport are explored
in details. We have analytically derived the conditions for the edge states for
a bilayer KM nanoribbon and show how these modes decay for lattice sites inside
the bulk. It is particularly interesting to note that for a finite-size ribbon
an even number of zigzag ribbon hosts a finite energy gap at the Dirac points,
while the odd ones do not. This asymmetry is present both in presence and
absence of a bias voltage that may exist between the layers. The interlayer
Rashba spin-orbit coupling, along with the intralayer intrinsic spin-orbit and
intralayer Rashba spin-orbit couplings seem to destroy the quantum spin Hall
(QSH) phase where the QSH phase is identified by the presence of a conductance
plateau (of magnitude 4e/h) in the vicinity of zero Fermi energy. The plateau
is sensitive to the values of the spin-orbit coupling parameters. Further, the
spin polarized conductance data reveal that a bilayer KM ribbon is found to be
more efficient for spintronic applications compared to a monolayer graphene.
Finally, a quick check with experiments is done via computing the effective
mass of electrons.Comment: 12 page
Stacking boundaries and transport in bilayer graphene
Pristine bilayer graphene behaves in some instances as an insulator with a
transport gap of a few meV. This behaviour has been interpreted as the result
of an intrinsic electronic instability induced by many-body correlations.
Intriguingly, however, some samples of similar mobility exhibit good metallic
properties, with a minimal conductivity of the order of . Here we
propose an explanation for this dichotomy, which is unrelated to electron
interactions and based instead on the reversible formation of boundaries
between stacking domains (`solitons'). We argue, using a numerical analysis,
that the hallmark features of the previously inferred many-body insulating
state can be explained by scattering on boundaries between domains with
different stacking order (AB and BA). We furthermore present experimental
evidence, reinforcing our interpretation, of reversible switching between a
metallic and an insulating regime in suspended bilayers when subjected to
thermal cycling or high current annealing.Comment: 13 pages, 15 figures. Published version (Nano Letters
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