2,319 research outputs found
Relation between dispersion lines and conductance of telescoped armchair double-wall nanotubes analyzed using perturbation formulas and first-principles calculations
The Landauer's formula conductance of the telescoped armchair nanotubes is
calculated with the Hamiltonian defined by first-principles calculations
(SIESTA code). Herein, partially extracting the inner tube from the outer tube
is called 'telescoping'. It shows a rapid oscillation superposed on a slow
oscillation as a function of discrete overlap length with an integer
variable and the lattice constant . Considering the interlayer
Hamiltonian as a perturbation, we obtain the approximate formula of the
amplitude of the slow oscillation as where is
the effective interlayer interaction and is the band split
without interlayer interaction. The approximate formula is related to the
Thouless number of the dispersion lines.Comment: 9 figure
Double- Order in a Frustrated Random Spin System
We use the three-dimensional Heisenberg model with site randomness as an
effective model of the compound Sr(FeMn)O. The model consists
of two types of ions that correspond to Fe and Mn ions. The nearest-neighbor
interactions in the ab-plane are antiferromagnetic. The nearest-neighbor
interactions along the c-axis between Fe ions are assumed to be
antiferromagnetic, whereas other interactions are assumed to be ferromagnetic.
From Monte Carlo simulations, we confirm the existence of the
double- ordered phase characterized by two wave numbers,
and . We also identify the spin ordering pattern in
the double- ordered phase.Comment: 5pages, 3figure
The effect of supersymmetry breaking in the Mass Varying Neutrinos
We discuss the effect of the supersymmetry breaking on the Mass Varying
Neutrinos(MaVaNs) scenario. Especially, the effect mediated by the
gravitational interaction between the hidden sector and the dark energy sector
is studied. A model including a chiral superfield in the dark sector and the
right handed neutrino superfield is proposed. Evolutions of the neutrino mass
and the equation of state parameter are presented in the model. It is remarked
that only the mass of a sterile neutrino is variable in the case of the
vanishing mixing between the left-handed and a sterile neutrino on cosmological
time scale. The finite mixing makes the mass of the left-handed neutrino
variable.Comment: 6 pages, 7 figures, RevTeX4, references added, discussions and
figures revise
Spin-state transition and phase separation in multi-orbital Hubbard model
We study spin-state transition and phase separation involving this transition
based on the milti-orbital Hubbard model. Multiple spin states are realized by
changing the energy separation between the two orbitals and the on-site Hund
coupling. By utilizing the variational Monte-Carlo simulation, we analyze the
electronic and magnetic structures in hole doped and undoped states. Electronic
phase separation occurs between the low-spin band insulating state and the
high-spin ferromagnetic metallic one. Difference of the band widths in the two
orbitals is of prime importance for the spin-state transition and the phase
separation.Comment: 5 pages, 5 figure
More anomaly-free models of six-dimensional gauged supergravity
We construct a huge number of anomaly-free models of six-dimensional N =
(1,0) gauged supergravity. The gauge groups are products of U(1) and SU(2), and
every hyperino is charged under some of the gauge groups. It is also found that
the potential may have flat directions when the R-symmetry is diagonally gauged
together with another gauge group. In an appendix, we determine the
contribution to the global SU(2) anomaly from symplectic Majorana Weyl fermions
in six dimensions.Comment: 20 pages, v3: published versio
Nonlinearly Realized Extended Supergravity
We provide nonlinear realization of supergravity with an arbitrary number of
supersymmetries by means of coset construction. The number of gravitino degrees
of freedom counts the number of supersymmetries, which will be possibly probed
in future experiments. We also consider goldstino embedding in the construction
to discuss the relation to nonlinear realization with rigid supersymmetries.Comment: 19 page
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