3,736 research outputs found
Layer Antiferromagnetic State in Bilayer Graphene : A First-Principle Investigation
The ground state of bilayer graphene is investigated by the density
functional calculations with local spin density approximation. We find a ground
state with layer antiferromagnetic ordering, which has been suggested by former
studies based on simplified model. The calculations prove that the layer
antiferromagnetic state (LAF) is stable even if the remote hopping and nonlocal
Coulomb interaction are included. The gap of the LAF state is about 1.8 meV,
comparable to the experimental value. The surface magnetism in BLG is of the
order of
Flat band electrons and interactions in rhombohedral trilayer graphene
Multilayer graphene systems with a rhombohedral stacking order harbor nearly
flat bands in their single-particle spectrum. We propose ansatz states to
describe the surface-localized states of flat band electrons. The absence of
kinetic dispersion near the fermi level leaves the interaction as a dominate
mechanism to govern the low energy physics of a low density electron system. We
build up an effective lattice model in two interacting low-energy bands, where
the full terms of the Coulomb interaction, including those long-range and
off-diagonal parts, have been considered. The interaction matrix coefficients
in the many-body Hamiltonian model are directly calculated for a trilayer
system using orthonormal Wannier basis. We then present a flat-band projection
to yield an interaction-only lattice model for flat band electrons. We find
that this limited model might energetically favor a ferromagnetic quantum
crystal under certain conditions.Comment: 8 pages, 3 figures, 3 tables. add journal reference and some
discussions in the context. arXiv admin note: text overlap with
arXiv:1108.008
Half Metallic Bilayer Graphene
Charge neutral bilayer graphene has a gapped ground state as transport
experiments demonstrate. One of the plausible such ground states is layered
antiferromagnetic spin density wave (LAF) state, where the spins in top and
bottom layers have same magnitude with opposite directions. We propose that
lightly charged bilayer graphene in an electric field perpendicular to the
graphene plane may be a half metal as a consequence of the inversion and
particle-hole symmetry broken in the LAF state. We show this explicitly by
using a mean field theory on a 2-layer Hubbard model for the bilayer graphene.Comment: 4+ pages, 4 figure
Study on shear resistance of full-scale PC box girder reinforced by SPCCS method
Steel plate and concrete composite strengthening (SPCCS) method is developed on the basis of steel and concrete composite girder, the process of which mainly includes welding studs on the reinforcing steel plates, planting rebars in the original concrete, and casting concrete between the original structure and steel plates, thus the new and existing concrete can work together. It can improve both the bearing capacity and stiffness of bridge significantly. In order to investigate the shear resistance of concrete girder reinforced by SPCCS method, two full-scale damaged box girder released from an actual bridge are tested for contrast, one without reinforcement and the other is reinforced by SPCCS method. The shear mechanical behavior and failure mode before and after reinforcement are obtained and analyzed. Furthermore, the shear mechanism and calculation formula of shear capacity for box girder reinforced by SPCCS method are presented. The comparisons show that the calculation results are in good agreement with the test results
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