3,266 research outputs found
Half-Metallic Graphene Nanoribbons
Electrical current can be completely spin polarized in a class of materials
known as half-metals, as a result of the coexistence of metallic nature for
electrons with one spin orientation and insulating for electrons with the
other. Such asymmetric electronic states for the different spins have been
predicted for some ferromagnetic metals - for example, the Heusler compounds-
and were first observed in a manganese perovskite. In view of the potential for
use of this property in realizing spin-based electronics, substantial efforts
have been made to search for half-metallic materials. However, organic
materials have hardly been investigated in this context even though
carbon-based nanostructures hold significant promise for future electronic
device. Here we predict half-metallicity in nanometre-scale graphene ribbons by
using first-principles calculations. We show that this phenomenon is realizable
if in-plane homogeneous electric fields are applied across the zigzag-shaped
edges of the graphene nanoribbons, and that their magnetic property can be
controlled by the external electric fields. The results are not only of
scientific interests in the interplay between electric fields and electronic
spin degree of freedom in solids but may also open a new path to explore
spintronics at nanometre scale, based on graphene
Charge-spin correlation in van der Waals antiferromagenet NiPS3
Strong charge-spin coupling is found in a layered transition-metal
trichalcogenide NiPS3, a van derWaals antiferromagnet, from our study of the
electronic structure using several experimental and theoretical tools:
spectroscopic ellipsometry, x-ray absorption and photoemission spectroscopy,
and density-functional calculations. NiPS3 displays an anomalous shift in the
optical spectral weight at the magnetic ordering temperature, reflecting a
strong coupling between the electronic and magnetic structures. X-ray
absorption, photoemission and optical spectra support a self-doped ground state
in NiPS3. Our work demonstrates that layered transition-metal trichalcogenide
magnets are a useful candidate for the study of correlated-electron physics in
two-dimensional magnetic material.Comment: 6 pages, 3 figur
Creation and evolution of magnetic helicity
Projecting a non-Abelian SU(2) vacuum gauge field - a pure gauge constructed
from the group element U - onto a fixed (electromagnetic) direction in isospace
gives rise to a nontrivial magnetic field, with nonvanishing magnetic helicity,
which coincides with the winding number of U. Although the helicity is not
conserved under Maxwell (vacuum) evolution, it retains one-half its initial
value at infinite time.Comment: Clarifying remarks and references added; 12 pages, 1 figure using
BoxedEPSF, REVTeX macros; submitted to Phys Rev D; email to
[email protected]
Direct observation of localized defect states in semiconductor nanotube junctions
Scanning tunneling microscopy of semiconductor-semiconductor carbon nanotube junctions with different band gaps was studied. Characteristic features of the wave functions at different energy levels were exhibited in the atomically resolved scanning tunneling microscopy. The experimental observations in terms of the pentagon-heptagon defects in the junction were interpreted.open888
Quantum teleportation via a W state
We investigate two schemes of the quantum teleportation with a state,
which belongs to a different class from a Greenberger-Horne-Zeilinger class. In
the first scheme, the state is shared by three parties one of whom, called
a sender, performs a Bell measurement. It is shown that quantum information of
an unknown state is split between two parties and recovered with a certain
probability. In the second scheme, a sender takes two particles of the
state and performs positive operator valued measurements in two ways. For two
schemes, we calculate the success probability and the average fidelity. We show
that the average fidelity of the second scheme cannot exceed that of the first
one.Comment: 7 pages, 1 figur
Meson Exchange Effect on Color Superconductivity
We investigate the effects of pion and gluon exchanges on the formation of
two-flavor color superconductivity at moderate density, . The
chiral quark model proposed by Manohar and Georgi containing pions as well as
gluons is employed to show that the pion exchange reduces substantially the
value of the superconducting gap gotten with the gluon exchange only. It turns
out that the pion exchanges produce a repulsion between quark-quark pair in a
spin and isospin singlet state.
We suggest that the phase consisiting of pions, gluons and quarks is one of
the candidates of in-medium QCD phase at moderate density.Comment: 8 pages, 1 figure, minor correction
Current reversal with type-I intermittency in deterministic inertia ratchets
The intermittency is investigated when the current reversal occurs in a
deterministic inertia ratchet system. To determine which type the intermittency
belongs to, we obtain the return map of velocities of particle using
stroboscopic recording, and numerically calculate the distribution of average
laminar length . The distribution follows the scaling law of , the characteristic relation of type-I
intermittency.Comment: 4 pages, 7 figure
Negative Thermal Expansion Coefficient of Graphene Measured by Raman Spectroscopy
The thermal expansion coefficient (TEC) of single-layer graphene is estimated
with temperature-dependent Raman spectroscopy in the temperature range between
200 and 400 K. It is found to be strongly dependent on temperature but remains
negative in the whole temperature range, with a room temperature value of
-8.0x10^{-6} K^{-1}. The strain caused by the TEC mismatch between graphene and
the substrate plays a crucial role in determining the physical properties of
graphene, and hence its effect must be accounted for in the interpretation of
experimental data taken at cryogenic or elevated temperatures.Comment: 17 pagese, 3 figures, and supporting information (4 pages, 3
figures); Nano Letters, 201
Anisotropic behaviors of massless Dirac fermions in graphene under periodic potential
Charge carriers of graphene show neutrino-like linear energy dispersions as
well as chiral behavior near the Dirac point. Here we report highly unusual and
unexpected behaviors of these carriers in applied external periodic potentials,
i.e., in graphene superlattices. The group velocity renormalizes highly
anisotropically even to a degree that it is not changed at all for states with
wavevector in one direction but is reduced to zero in another, implying the
possibility that one can make nanoscale electronic circuits out of graphene not
by cutting it but by drawing on it in a non-destructive way. Also, the type of
charge carrier species (e.g. electron, hole or open orbit) and their density of
states vary drastically with the Fermi energy, enabling one to tune the Fermi
surface-dominant properties significantly with gate voltage. These results
address the fundamental question of how chiral massless Dirac fermions
propagate in periodic potentials and point to a new possible path for nanoscale
electronics.Comment: 10 pages, 9 figure
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