14,813 research outputs found
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
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
The long-lasting optical afterglow plateau of short burst GRB 130912A
The short burst GRB 130912A was detected by Swift, Fermi satellites and
several ground-based optical telescopes. Its X-ray light curve decayed with
time normally. The optical emission, however, displayed a long term plateau,
which is the longest one in current short GRB observations. In this work we
examine the physical origin of the X-ray and optical emission of this peculiar
event. We find that the canonical forward shock afterglow emission model can
account for the X-ray and optical data self-consistently and the energy
injection model that has been widely adopted to interpret the
shallowly-decaying afterglow emission is not needed. We also find that the
burst was born in a very-low density interstellar medium, consistent with the
compact object merger model. Significant fractions of the energy of the forward
shock have been given to accelerate the non-thermal electrons and amplify the
magnetic fields (i.e., and , respectively), which are much larger than those inferred in most short
burst afterglow modeling and can explain why the long-lasting optical afterglow
plateau is rare in short GRBs.Comment: 5 pages, 2 figure
Bis(3-hydroxypropanaminium) naphthalene-1,5-disulfonate
In the title molecular salt, 2C3H10NO+·C10H6O6S2
2−, the cations and anions are associated via N—H⋯O and O—H⋯O hydrogen-bonding interactions, giving rise to a three-dimensional structure with zigzag rows of cations lying between rows of anions. The asymmetric unit contains one cation and one half-anion, which is related to the remainder of the molecule by an inversion center
- …