870 research outputs found
Modulation of Kekul\'e adatom ordering due to strain in graphene
Full text linkIntervalley scattering of carriers in graphene at `top' adatoms may give rise
to a hidden Kekul\'e ordering pattern in the adatom positions. This ordering is
the result of a rapid modulation in the electron-mediated interaction between
adatoms at the wavevector , which has been shown experimentally and
theoretically to dominate their spatial distribution. Here we show that the
adatom interaction is extremely sensitive to strain in the supporting graphene,
which leads to a characteristic spatial modulation of the Kekul\'e order as a
function of adatom distance. Our results suggest that the spatial distributions
of adatoms could provide a way to measure the type and magnitude of strain in
graphene and the associated pseudogauge field with high accuracy.Comment: 9 pages, 7 figure
Band topology and quantum spin Hall effect in bilayer graphene
Full text linkWe consider bilayer graphene in the presence of spin orbit coupling, to
assess its behavior as a topological insulator. The first Chern number for
the energy bands of single and bilayer graphene is computed and compared. It is
shown that for a given valley and spin, in a bilayer is doubled with
respect to the monolayer. This implies that bilayer graphene will have twice as
many edge states as single layer graphene, which we confirm with numerical
calculations and analytically in the case of an armchair terminated surface.
Bilayer graphene is a weak topological insulator, whose surface spectrum is
susceptible to gap opening under spin-mixing perturbations. We also assess the
stability of the associated topological bulk state of bilayer graphene under
various perturbations. Finally, we consider an intermediate situation in which
only one of the two layers has spin orbit coupling, and find that although
individual valleys have non-trivial Chern numbers, the spectrum as a whole is
not gapped, so that the system is not a topological insulator.Comment: 9 pages. 9 figures include
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