14,648 research outputs found
Structural and electronic transformation in low-angle twisted bilayer graphene
Experiments on bilayer graphene unveiled a fascinating realization of
stacking disorder where triangular domains with well-defined Bernal stacking
are delimited by a hexagonal network of strain solitons. Here we show by means
of numerical simulations that this is a consequence of a structural
transformation of the moir\'{e} pattern inherent of twisted bilayer graphene
taking place at twist angles below a crossover angle
. The transformation is governed by the interplay
between the interlayer van der Waals interaction and the in-plane strain field,
and is revealed by a change in the functional form of the twist energy density.
This transformation unveils an electronic regime characteristic of vanishing
twist angles in which the charge density converges, though not uniformly, to
that of ideal bilayer graphene with Bernal stacking. On the other hand, the
stacking domain boundaries form a distinct charge density pattern that provides
the STM signature of the hexagonal solitonic network.Comment: published version with supplementary materia
Topological Aspects of Charge-Carrier Transmission across Grain Boundaries in Graphene
We systematically investigate the transmission of charge carriers across the
grain-boundary defects in polycrystalline graphene by means of the
Landauer-B\"uttiker formalism within the tight-binding approximation.
Calculations reveal a strong suppression of transmission at low energies upon
decreasing the density of dislocations with the smallest Burger's vector
. The observed transport anomaly is explained from the point
of view of back-scattering due to localized states of topological origin. These
states are related to the gauge field associated with all dislocations
characterized by with ().
Our work identifies an important source of charge-carrier scattering caused by
topological defects present in large-area graphene samples produced by chemical
vapor deposition.Comment: 5 pages, 4 figure
Non-perturbative effects on seven-brane Yukawa couplings
We analyze non-perturbative corrections to the superpotential of seven-brane
gauge theories on type IIB and F-theory warped Calabi-Yau compactifications. We
show in particular that such corrections modify the holomorphic Yukawa
couplings by an exponentially suppressed contribution, generically solving the
Yukawa rank-one problem present in F-theory local models. We provide explicit
expressions for the non-perturbative correction to the seven-brane
superpotential, and check that it is related to a non-commutative deformation
to the tree-level superpotential via the Seiberg-Witten map.Comment: 4 pages. v2: minor changes, footnotes and citations added. Version to
be published in PR
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