10,194 research outputs found
Array of Josephson junctions with a non-sinusoidal current-phase relation as a model of the resistive transition of unconventional superconductors
An array of resistively and capacitively shunted Josephson junctions with
nonsinusoidal current-phase relation is considered for modelling the transition
in high-T superconductors. The emergence of higher harmonics, besides the
simple sinusoid , is expected for dominant \emph{d}-wave
symmetry of the Cooper pairs, random distribution of potential drops, dirty
grains, or nonstationary conditions. We show that additional cosine and sine
terms act respectively by modulating the global resistance and by changing the
Josephson coupling of the mixed superconductive-normal states. First, the
approach is applied to simulate the transition in disordered granular
superconductors with the weak-links characterized by nonsinusoidal
current-phase relation. In granular superconductors, the emergence of
higher-order harmonics affects the slope of the transition. Then, arrays of
intrinsic Josephson junctions, naturally formed by the CuO planes in
cuprates, are considered. The critical temperature suppression, observed at
values of hole doping close to , is investigated. Such suppression,
related to the sign change and modulation of the Josephson coupling across the
array, is quantified in terms of the intensities of the first and second
sinusoids of the current-phase relation. Applications are envisaged for the
design and control of quantum devices based on stacks of intrinsic Josephson
junctions.Comment: Added: comparison with experiments; reference
Quark model description of the tetraquark state X(3872) in a relativistic constituent quark model with infrared confinement
We explore the consequences of treating the X(3872) meson as a tetraquark
bound state. As dynamical framework we employ a relativistic constituent quark
model which includes infrared confinement in an effective way. We calculate the
decay widths of the observed channels X-> Jpsi+2\pi (3\pi) and X-> \bar
D0+D0+\pi0 via the intermediate off--shell states X-> Jpsi+\rho(\omega) and X->
\bar D + D*. For reasonable values of the size parameter of the X(3872) we find
consistency with the available experimental data. We also discuss the possible
impact of the X(3872) in a s-channel dominance description of the
Jpsi-dissociation cross section.Comment: 9 pages, 5 figures; discussion and references added, accepted in
Phys. Rev.
The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/d-wave superconductor contact
The influence of phase shifts of electron waves passing through and reflected
by the potential barrier on the Andreev reflection in a
ferromagnet/isolator/d-wave superconductor (FIS) contact is studied. It is
found that in a superconductor the surface spin-dependent Andreev bound states
inside the superconducting gap are formed as a result of the interference of
electron-like and hole-like quasiparticles due to repeated Andreev reflections.
The peak in the conductance of the FIS contact at the zero potential for the
(110)-oriented superconductor disappears rapidly as the polarization of a
ferromagnet increases, whereas for the (100)-oriented superconductor it
appears. The physical reason for this behavior of conductance is discussed.Comment: 8 pages, 4 figure
The hard scale in the exclusive rho-meson production in diffractive DIS
We re-examine the issue of the pQCD factorization scale in the exclusive rho
production in diffractive DIS from the k_t-factorization point of view. We find
that this scale differs significantly from, and possesses much flatter Q^2
behavior than widely used value (Q^2 + m_\rho^2)/4. With these results in mind,
we discuss the Q^2 shape of the rho meson production cross section. We
introduce rescaled cross sections, which might provide further insight into the
dynamics of rho production. We also comment on the recent ZEUS observation of
energy-independent ratio sigma(gamma* p --> rho p) / sigma_{tot}(gamma*p).Comment: 14 pages, 7 eps figure
Influence of Primary Cosmic Radiation Mass Composition on the Estimation of Eas Energy
At the Yakutsk EAS array E_em is determined by using measurements of EAS
Cherenkov light flux and charged particle flux. It is known from calculations
that these characteristics depend on a sort of primary particle and, therefore,
the estimation of E_em depends on a primary particle mass. In the work the
dependence of the E_em/E_0 ratio on the energy is given and experimental data
are compared with calculations by the QGSJET model. The calculations have been
carried out for the primary proton and iron nucleus. The average calculated
meaning of the value of E_em/E_0 ratio (between the proton and iron nucleus)
within experimental errors is in agreement with experimental data that doesnt
contradict to the mixed mass composition of primary cosmic radiation.Comment: 19th European Cosmic Ray Symposium. Aug 30 - Sep 3 2004, Florence,
Italy. 3 pages, 1 figure. Subbmitted for publication in International Journal
of Modern Physics
Fluctuations of Xmax and Primary Particle Mass Composition in the Range of Energy 5 10^{17} - 3 10^{19} ev by Yakutsk Data
The experimental distributions of \Xmax obtained with the Yakutsk EAS array
at fixed energies of , and
eV are analysed. A recent version of the QGSJET model is used as a tool of our
analysis. In the framework of this model, the most adequate mass composition of
primary particles satisfying the experimental data on \Xmax is selected.Comment: 19th European Cosmic Ray Symposium, Aug 30 - Sep 3 2004, Florence,
Italy. 3 pages, 1 figure. Submitted for publication in International Journal
of Modern Physics
One-photon decay of the tetraquark state in a relativistic constituent quark model with infrared confinement
We further explore the consequences of treating the X(3872) meson as a
tetraquark bound state by analyzing its one-photon decay X => \gamma + J/psi in
the framework of our approach developed in previous papers which incorporates
quark confinement in an effective way. To introduce electromagnetism we gauge a
nonlocal effective Lagrangian describing the interaction of the X(3872) meson
with its four constituent quarks by using the P-exponential path-independent
formalism. We calculate the matrix element of the transition X => \gamma+ J/psi
and prove its gauge invariance. We evaluate the X=> \gamma + J/psi decay width
and the longitudinal/transverse composition of the J/psi in this decay. For a
reasonable value of the size parameter of the X(3872) meson we find consistency
with the available experimental data. We also calculate the helicity and
multipole amplitudes of the process, and describe how they can be obtained from
the covariant transition amplitude by covariant projection.Comment: 13 pages, 5 figures. Typos corrected, version matching the one
published in PR
Non-Fraunhofer patterns of the anharmonic Josephson current influenced by a strong interfacial pair breaking
In the junctions with a strong Josephson coupling and a pronounced
interfacial pair breaking, the magnetic interference patterns of the Josephson
current are shown to differ substantially from the standard Fraunhofer shape.
The Fraunhofer pattern occurs, when Josephson couplings are weak. The narrow
peak of the critical current, centered at the zero magnetic field, and the
suppressed hills at finite field values are the characteristic features of the
non-Fraunhofer magnetic field modulation of the critical current, obtained in
this paper.Comment: 5 pages, 4 figure
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