7,878 research outputs found
Crystals for Demazure Modules of Classical Affine Lie Algebras
We study, in the path realization, crystals for Demazure modules of affine
Lie algebras of types . We find a special sequence of
affine Weyl group elements for the selected perfect crystal, and show if the
highest weight is l\La_0, the Demazure crystal has a remarkably simple
structure.Comment: Latex, 28 page
Transition state method and Wannier functions
We propose a computational scheme for materials where standard Local Density
Approximation (LDA) fails to produce a satisfactory description of excitation
energies. The method uses Slater's "transition state" approximation and Wannier
functions basis set. We define a correction to LDA functional in such a way
that its variation produces one-electron energies for Wannier functions equal
to the energies obtained in "transition state" constrained LDA calculations. In
the result eigenvalues of the proposed functional could be interpreted as
excitation energies of the system under consideration. The method was applied
to MgO, Si, NiO and BaBiO and gave an improved agreement with experimental
data of energy gap values comparing with LDA.Comment: 13 pages, 6 figures, 1 tabl
Pressure-induced enhancement of superconductivity and superconducting-superconducting transition in CaC
We measured the electrical resistivity, , of superconducting
CaC at ambient and high pressure up to 16 GPa. For 8 GPa, we found
a large increase of with pressure from 11.5 up to 15.1 K. At 8 GPa,
drops and levels off at 5 K above 10 GPa. Correspondingly, the residual
increases by 200 times and the behavior
becomes flat. The recovery of the pristine behavior after depressurization is
suggestive of a phase transition at 8 GPa between two superconducting phases
with good and bad metallic properties, the latter with a lower and more
static disorder
NMR Evidence for Antiferromagnetic Transition in the Single-Component Molecular System, [Cu(tmdt)]
The magnetic state of the single-component molecular compound,
[Cu(tmdt)], is investigated by means of H-NMR. An abrupt spectral
broadening below 13 K and a sharp peak in nuclear spin-lattice relaxation rate,
, at 13 K are observed as clear manifestations of a second-order
antiferromagnetic transition, which is consistent with the previously reported
magnetic susceptibility and EPR measurement. The ordered moment is estimated at
/molecule. The temperature-dependence of
above the transition temperature indicates one-dimensional spin
dynamics and supports that the spins are on the central part of the molecule
differently from other isostructural compounds.Comment: 13pages, 5 figure
Magnetotransport in Sr3PbO antiperovskite with three-dimensional massive Dirac electrons
Novel topological phenomena are anticipated for three-dimensional (3D) Dirac
electrons. The magnetotransport properties of cubic
antiperovskite, theoretically proposed to be a 3D massive Dirac electron
system, are studied. The measurements of Shubnikov-de Haas oscillations and
Hall resistivity indicate the presence of a low density ( ) of holes with an extremely small cyclotron mass of
0.01-0.06. The magnetoresistance is linear in
magnetic field with the magnitude independent of temperature. These results
are fully consistent with the presence of 3D massive Dirac electrons in . The chemical flexibility of the antiperovskites and our findings
in the family member, , point to their potential as a model
system in which to explore exotic topological phases
Photometric redshift accuracy in AKARI Deep Surveys
We investigate the photometric redshift accuracy achievable with the AKARI
infrared data in deep multi-band surveys, such as in the North Ecliptic Pole
field. We demonstrate that the passage of redshifted policyclic aromatic
hydrocarbons and silicate features into the mid-infrared wavelength window
covered by AKARI is a valuable means to recover the redshifts of starburst
galaxies. To this end we have collected a sample of ~60 galaxies drawn from the
GOODS-North Field with spectroscopic redshift 0.5<~z_spec<~1.5 and photometry
from 3.6 to 24 micron, provided by the Spitzer, ISO and AKARI satellites. The
infrared spectra are fitted using synthetic galaxy Spectral Energy
Distributions which account for starburst and active nuclei emission. For ~90%
of the sources in our sample the redshift is recovered with an accuracy
|z_phot-z_spec|/(1+z_spec)<~10%. A similar analysis performed on different sets
of simulated spectra shows that the AKARI infrared data alone can provide
photometric redshifts accurate to |z_phot-z_spec|/(1+z_spec)<~10% (1-sigma) at
z<~2. At higher redshifts the PAH features are shifted outside the wavelength
range covered by AKARI and the photo-z estimates rely on the less prominent 1.6
micron stellar bump; the accuracy achievable in this case on (1+z) is ~10-15%,
provided that the AGN contribution to the infrared emission is subdominant. Our
technique is no more prone to redshift aliasing than optical-uv photo-z, and it
may be possible to reduce this aliasing further with the addition of
submillimetre and/or radio data.Comment: 27 pages, 12 figures, 4 tables. Accepted for publication on MNRA
Non-perturbative corrections to mean-field behavior: spherical model on spider-web graph
We consider the spherical model on a spider-web graph. This graph is
effectively infinite-dimensional, similar to the Bethe lattice, but has loops.
We show that these lead to non-trivial corrections to the simple mean-field
behavior. We first determine all normal modes of the coupled springs problem on
this graph, using its large symmetry group. In the thermodynamic limit, the
spectrum is a set of -functions, and all the modes are localized. The
fractional number of modes with frequency less than varies as for tending to zero, where is a constant. For an
unbiased random walk on the vertices of this graph, this implies that the
probability of return to the origin at time varies as ,
for large , where is a constant. For the spherical model, we show that
while the critical exponents take the values expected from the mean-field
theory, the free-energy per site at temperature , near and above the
critical temperature , also has an essential singularity of the type
.Comment: substantially revised, a section adde
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