397 research outputs found
Optical sum rule violation, superfluid weight and condensation energy in the cuprates
The model of hole superconductivity predicts that the superfluid weight in
the zero-frequency -function in the optical conductivity has an
anomalous contribution from high frequencies, due to lowering of the system's
kinetic energy upon entering the superconducting state. The lowering of kinetic
energy, mainly in-plane in origin, accounts for both the condensation energy of
the superconductor as well as an increased potential energy due to larger
Coulomb repulsion in the paired state. It leads to an apparent violation of the
conductivity sum rule, which in the clean limit we predict to be substantially
larger for in-plane than for c-axis conductivity. However, because cuprates are
in the dirty limit for c-axis transport, the sum rule violation is found to be
greatly enhanced in the c-direction. The model predicts the sum rule violation
to be largest in the underdoped regime and to decrease with doping, more
rapidly in the c-direction that in the plane. So far, experiments have detected
sum rule violation in c-axis transport in several cuprates, as well as a
decrease and disappearance of this violation for increasing doping, but no
violation in-plane. We explore the predictions of the model for a wide range of
parameters, both in the absence and in the presence of disorder, and the
relation with current experimental knowledge.Comment: submitted to Phys.Rev.
De rol van de overheid
Gesprek met als onderwerp: De rol van de overheid in de huidige verzorgingsstaa
The relative error of calculations at the Pöschl-Teller model potential for the planar channeled muon
In the framework of quantum mechanics, we investigate muon channeling in the Si (200) crystal. The transverse energy levels and wave functions are obtained for the Pöschl-Teller and the Doyle-Turner potentials. Comparative analysis demonstrates that analytical results of calculations obtained on the base of the Pöschl-Teller potential are in a good agreement with the numerical results of calculations in the Doyle-Turner model for the low energy levels. These results for the muon with rest mass m[mu] and relativistic factor [gamma] are valid for any particle with elementary charge and rest mass m and relativistic factor [gamma][m]=[gamma](m[mu]/m). Therefore, our results can be useful for the preparation and performing the experimental investigation of the various phenomena accompanying particle channeling
Magnetic and pair correlations of the Hubbard model with next-nearest-neighbor hopping
A combination of analytical approaches and quantum Monte Carlo simulations is
used to study both magnetic and pairing correlations for a version of the
Hubbard model that includes second-neighbor hopping as a
model for high-temperature superconductors. Magnetic properties are analyzed
using the Two-Particle Self-Consistent approach. The maximum in magnetic
susceptibility as a function of doping appears both at finite
and at but for two totally different physical reasons. When
, it is induced by antiferromagnetic correlations while at
it is a band structure effect amplified by interactions.
Finally, pairing fluctuations are compared with -matrix results to
disentangle the effects of van Hove singularity and of nesting on
superconducting correlations. The addition of antiferromagnetic fluctuations
increases slightly the -wave superconducting correlations despite the
presence of a van Hove singularity which tends to decrease them in the
repulsive model. Some aspects of the phase diagram and some subtleties of
finite-size scaling in Monte Carlo simulations, such as inverted finite-size
dependence, are also discussed.Comment: Revtex, 8 pages + 15 uuencoded postcript figure
The beta-beta two neutrino decay in 48Ca
A schematic study of the -decay of is made in a
shell-model approach. The emphasis is especially put on the role of the
spin-orbit potential in relation with the contribution of other terms in the
strong interaction. This is discussed with a particular attention to the
behavior of these ones under the SU(4) symmetry. Different methods in
calculating the transition amplitude are also looked at with the aim to
determine their reliability and, eventually, why they don't work. Further
aspects relative to the failure of the Operator Expansion Method to reproduce
the results of more elaborate calculations are examined.Comment: 24 pages, 5 figure
Symmetry breaking in the Hubbard model at weak coupling
The phase diagram of the Hubbard model is studied at weak coupling in two and
three spatial dimensions. It is shown that the Neel temperature and the order
parameter in d=3 are smaller than the Hartree-Fock predictions by a factor of
q=0.2599. For d=2 we show that the self-consistent (sc) perturbation series
bears no relevance to the behavior of the exact solution of the Hubbard model
in the symmetry-broken phase. We also investigate an anisotropic model and show
that the coupling between planes is essential for the validity of
mean-field-type order parameters
Stein structures and holomorphic mappings
We prove that every continuous map from a Stein manifold X to a complex
manifold Y can be made holomorphic by a homotopic deformation of both the map
and the Stein structure on X. In the absence of topological obstructions the
holomorphic map may be chosen to have pointwise maximal rank. The analogous
result holds for any compact Hausdorff family of maps, but it fails in general
for a noncompact family. Our main results are actually proved for smooth almost
complex source manifolds (X,J) with the correct handlebody structure. The paper
contains another proof of Eliashberg's (Int J Math 1:29--46, 1990) homotopy
characterization of Stein manifolds and a slightly different explanation of the
construction of exotic Stein surfaces due to Gompf (Ann Math 148 (2):619--693,
1998; J Symplectic Geom 3:565--587, 2005). (See also the related preprint
math/0509419).Comment: The original publication is available at http://www.springerlink.co
Electron Dynamics in NdCeCuO: Evidence for the Pseudogap State and Unconventional c-axis Response
Infrared reflectance measurements were made with light polarized along the a-
and c-axis of both superconducting and antiferromagnetic phases of electron
doped NdCeCuO. The results are compared to
characteristic features of the electromagnetic response in hole doped cuprates.
Within the CuO planes the frequency dependent scattering rate,
1/, is depressed below 650 cm; this behavior is a
hallmark of the pseudogap state. While in several hole doped compounds the
energy scales associated with the pseudogap and superconducting states are
quite close, we are able to show that in NdCeCuO
the two scales differ by more than one order of magnitude. Another feature of
the in-plane charge response is a peak in the real part of the conductivity,
, at 50-110 cm which is in sharp contrast with the
Drude-like response where is centered at . This
latter effect is similar to what is found in disordered hole doped cuprates and
is discussed in the context of carrier localization. Examination of the c-axis
conductivity gives evidence for an anomalously broad frequency range from which
the interlayer superfluid is accumulated. Compelling evidence for the pseudogap
state as well as other characteristics of the charge dynamics in
NdCeCuO signal global similarities of the cuprate
phase diagram with respect to electron and hole doping.Comment: Submitted to PR
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
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