8,564 research outputs found
Enhancing the area of a Raman atom interferometer using a versatile double-diffraction technique
IIn this paper we demonstrate a new scheme for Raman transitions which
realize a symmetric momentum-space splitting of , deflecting the
atomic wave-packets into the same internal state. Combining the advantages of
Raman and Bragg diffraction, we achieve a three pulse state labelled
interferometer, intrinsically insensitive to the main systematics and
applicable to all kind of atomic sources. This splitting scheme can be extended
to momentum transfer by a multipulse sequence and is implemented
on a interferometer. We demonstrate the area enhancement by
measuring inertial forces
Theory of High-Tc Superconducting Cuprates Based on Experimental Evidence
A model of superconductivity in layered high-temperature superconducting
cuprates is proposed, based on the extended saddle point singularities in the
electron spectrum, weak screening of the Coulomb interaction and
phonon-mediated interaction between electrons plus a small short -range
repulsion of Hund's, or spin-fluctuation, origin. This permits to explain the
large values of , features of the isotope effect on oxygen and copper, the
existence of two types of the order parameter, the peak in the inelastic
neutron scattering, the positive curvature of the upper critical field, as
function of temperature etc.Comment: RevTeX 3.x, 11 Postscript figures (included); send comments to
[email protected]
Meso-Nh simulations of the atmospheric flow above the Internal Antarctic Plateau
Mesoscale model such as Meso-Nh have proven to be highly reliable in
reproducing 3D maps of optical turbulence (see Refs. 1, 2, 3, 4) above
mid-latitude astronomical sites. These last years ground-based astronomy has
been looking towards Antarctica. Especially its summits and the Internal
Continental Plateau where the optical turbulence appears to be confined in a
shallow layer close to the icy surface. Preliminary measurements have so far
indicated pretty good value for the seeing above 30-35 m: 0.36" (see Ref. 5)
and 0.27" (see Refs. 6, 7) at Dome C. Site testing campaigns are however
extremely expensive, instruments provide only local measurements and
atmospheric modelling might represent a step ahead towards the search and
selection of astronomical sites thanks to the possibility to reconstruct 3D Cn2
maps over a surface of several kilometers. The Antarctic Plateau represents
therefore an important benchmark test to evaluate the possibility to
discriminate sites on the same plateau. Our group8 has proven that the analyses
from the ECMWF global model do not describe with the required accuracy the
antarctic boundary and surface layer in the plateau. A better description could
be obtained with a mesoscale meteorological model. In this contribution we
present the progress status report of numerical simulations (including the
optical turbulence - Cn2) obtained with Meso-Nh above the internal Antarctic
Plateau. Among the topic attacked: the influence of different configurations of
the model (low and high horizontal resolution), use of the grid-nesting
interactive technique, forecasting of the optical turbulence during some winter
nights.Comment: 12 pages, 4 figures, SPIE 2008 conferenc
Large isotope effect on in cuprates despite of a small electron-phonon coupling
We calculate the isotope coefficients and for the
superconducting critical temperature and the pseudogap temperature
in a mean-field treatment of the t-J model including phonons. The
pseudogap phase is identified with the -charge-density wave (-CDW) phase
in this model. Using the small electron-phonon coupling constant obtained previously in LDA calculations in YBaCuO,
is negative but negligible small whereas increases
from about 0.03 at optimal doping to values around 1 at small dopings in
agreement with the general trend observed in many cuprates. Using a simple
phase fluctuation model where the -CDW has only short-range correlations it
is shown that the large increase of at low dopings is rather universal
and does not depend on the existence of sharp peaks in the density of states in
the pseudogap state or on specific values of the phonon cutoff. It rather is
caused by the large depletion of spectral weight at low frequencies by the
-CDW and thus should also occur in other realizations of the pseudogap.Comment: 8 pages, 5 figures, to be publ. in PR
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