5,180 research outputs found
Theoretical Study on Transport Properties of Normal Metal - Zigzag Graphene Nanoribbon - Normal Metal Junctions
We investigate transport properties of the junctions in which the graphene
nanoribbon with the zigzag shaped edges consisting of the legs is
sandwiched by the two normal metals by means of recursive Green's function
method. The conductance and the transmission probabilities are found to have
the remarkable properties depending on the parity of . The singular
behaviors close to E=0 with being the Fermi energy are demonstrated. The
channel filtering is shown to occur in the case with even.Comment: 4 pages, 5 figure
Nonuniversal Shot Noise in Disordered Quantum Wires with Channel-Number Imbalance
The number of conducting channels for one propagating direction is equal to
that for the other direction in ordinary quantum wires. However, they can be
imbalanced in graphene nanoribbons with zigzag edges. Employing the model
system in which a degree of channel-number imbalance can be controlled, we
calculate the shot-noise power at zero frequency by using the
Boltzmann-Langevin approach. The shot-noise power in an ordinary diffusive
conductor is one-third of the Poisson value. We show that with increasing the
degree of channel-number imbalance, the universal one-third suppression breaks
down and a highly nonuniversal behavior of shot noise appears.Comment: 10 pages, 3 figure
Resonant X-ray Study on the Bi-Layered Perovskite Mn Oxide LaSr2Mn2O7
Charge and orbital ordering behaviors in the half doped bi-layered compound
LaSr2Mn2O7 have been studied by resonant and non-resonant X-ray scattering.
Three different order parameters, which correspond to the A-type
antiferromagnetic, a charge and an orbital ordered states, were observed by
measuring the magnetostriction and the superlattice peaks characterized by
wavevectors (1/2 1/2 0) and (1/4 1/4 0), respectively. The superlattice
reflections indicating the charge and orbital ordered states were observed
below 210 K. Both the intensities reach a maximum at 160 K on cooling and
become very weak below 100 K. The peak width of the charge ordered state agrees
with that of the orbital ordered state at all temperatures studied. These
results indicate that both the states originate from a single phase and that
the charge/orbital ordered islands with definite interfaces disperse in the
A-type antiferromagnetic phase. The dimensionality of the charge/orbital
ordered phase is discussed using this model.Comment: 9pages, 10 figure
Instabilities at [110] Surfaces of d_{x^2-y^2} Superconductors
We compare different scenarios for the low temperature splitting of the
zero-energy peak in the local density of states at (110) surfaces of
d_{x^2-y^2}-wave superconductors, observed by Covington et al.
(Phys.Rev.Lett.79 (1997), 277). Using a tight binding model in the
Bogolyubov-de Gennes treatment we find a surface phase transition towards a
time-reversal symmetry breaking surface state carrying spontaneous currents and
an s+id-wave state. Alternatively, we show that electron correlation leads to a
surface phase transition towards a magnetic state corresponding to a local spin
density wave state.Comment: 4 pages, 5 figure
Soliton Trap in Strained Graphene Nanoribbons
The wavefunction of a massless fermion consists of two chiralities,
left-handed and right-handed, which are eigenstates of the chiral operator. The
theory of weak interactions of elementally particle physics is not symmetric
about the two chiralities, and such a symmetry breaking theory is referred to
as a chiral gauge theory. The chiral gauge theory can be applied to the
massless Dirac particles of graphene. In this paper we show within the
framework of the chiral gauge theory for graphene that a topological soliton
exists near the boundary of a graphene nanoribbon in the presence of a strain.
This soliton is a zero-energy state connecting two chiralities and is an
elementally excitation transporting a pseudospin. The soliton should be
observable by means of a scanning tunneling microscopy experiment.Comment: 7 pages, 4 figure
Surface effects on the orbital order in the single layered manganite La0.5Sr1.5MnO4
We report the first observation of `orbital truncation rods' -- the
scattering arising from the termination of bulk orbital order at the surface of
a crystal. The x-ray measurements, performed on a cleaved, single-layered
perovskite, La0.5Sr1.5MnO4, reveal that while the crystallographic surface is
atomically smooth, the orbital `surface' is much rougher, with an r.m.s.
deviation from the average `surface' of ~0.7nm. The temperature dependence of
this scattering shows evidence of a surface-induced second order transition.Comment: 13 pages, 4 figure
Valley filter and valley valve in graphene
It is known that the lowest propagating mode in a narrow ballistic ribbon of
graphene may lack the twofold valley degeneracy of higher modes. Depending on
the crystallographic orientation of the ribbon axis, the lowest mode mixes both
valleys or lies predominantly in a single valley (chosen by the direction of
propagation). We show, using a tight-binding model calculation, that a
nonequilibrium valley polarization can be realized in a sheet of graphene, upon
injection of current through a ballistic point contact with zigzag edges. The
polarity can be inverted by local application of a gate voltage to the point
contact region. Two valley filters in series may function as an
electrostatically controlled ``valley valve'', representing a
zero-magnetic-field counterpart to the familiar spin valve.Comment: RevTeX, 4 pages, 5 figure
Magnetic Structure of Nano-Graphite Moebius Ribbon
We consider the electronic and magnetic properties of nanographite ribbon
with zigzag edges under the periodic or Moebius boundary conditions. The zigzag
nano-graphite ribbons possess edge localized states at the Fermi level which
cause a ferrimagnetic spin polarization localized at the edge sites even in the
very weak Coulomb interaction. The imposition of the Moebius boundary condition
makes the system non-AB-bipartite lattice, and depress the spin polarization,
resulting in the formation of a magnetic domain wall. The width of the magnetic
domain depends on the Coulomb interaction and narrows with increasing U/t.Comment: 4 pages; 6 figures; published at J. Phys. Soc. Jpn. Vol. 72 No. 5 pp.
998-1001 (2003
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