4,830 research outputs found
NJL interaction derived from QCD: vector and axial-vector mesons
In previous works effective non-local NJL model was
derived in the framework of the fundamental QCD. All the parameters of the
model are expressed through QCD parameters: current light quark mass and
average non-perturbative . The results for scalar and pseudo-scalar
mesons are in satisfactory agreement to existing data. In the present work the
same model without introduction of any additional parameters is applied for a
description of masses and strong decay widths of - and -mesons. The
results for both scalar and vector sectors agree with data with only one
adjusted parameter , with account of average ,
which is obtained in a previous work as well.Comment: 19 pages, 2 figures, 1 tabl
A Discrete Version of the Inverse Scattering Problem and the J-matrix Method
The problem of the Hamiltonian matrix in the oscillator and Laguerre basis
construction from the S-matrix is treated in the context of the algebraic
analogue of the Marchenko method.Comment: 11 pages. The Laguerre basis case is adde
Anatomy of point-contact Andreev reflection spectroscopy from the experimental point of view (review)
We review application of point-contact Andreev-reflection spectroscopy to
study elemental superconductors, where theoretical conditions for the smallness
of the point-contact size with respect to the characteristic lengths in the
superconductor can be satisfied. We discuss existing theoretical models and
identify new issues that have to be solved, especially when applying this
method to investigate more complex superconductors. We will also demonstrate
that some aspects of point-contact Andreev-reflection spectroscopy still need
to be addressed even when investigating ordinary metals.Comment: 20 pages, 18 figs. V2: Ref.60 and footnote 3 are added, a number of
minor fixe
Point Contact Spectroscopy of Superconducting Gap Anisotropy in Nickel Borocarbide Compound LuNi2B2C
Point contacts are used to investigate the anisotropy of the superconducting
energy gap in LuNi2B2C in the ab plane and along the c axis. It is shown that
the experimental curves should be described assuming that the superconducting
gap is non-uniformly distributed over the Fermi surface. The largest and the
smallest gaps have been estimated by two-gap fitting models. It is found that
the largest contribution to the point-contact conductivity in the c direction
is made by a smaller gap and, in the ab plane by a larger gap. The deviation
from the one-gap BCS model is pronounced in the temperature dependence of the
gap in both directions. The temperature range, where the deviation occurs, is
for the c direction approximately 1.5 times more than in the ab plane. The
\Gamma parameter, allowing quantitatively estimate the gap anisotropy by
one-gap fitting, in c direction is also about 1.5 times greater than in the ab
plane. Since it is impossible to describe satisfactorily such gap distribution
either by the one- or two-gap models, a continuous, dual-maxima model of gap
distribution over the Fermi surface should be used to describe
superconductivity in this material.Comment: 10 pages, 14 Figs, accepted in PR
Efficient Thermoelectric Materials Based on Solid Solutions of Mg2X Compounds (X = Si, Ge, Sn)
The silicides have obvious attractive characteristics that make them promising materials as thermoelectric energy converters. The constituting elements are abundant and have low price, many of compounds have good high temperature stability. Therefore, considerable efforts have been made, especially in the past 10 years, in order to develop efficient silicide-based thermoelectric materials. These efforts have culminated in creation of Mg2(Si-Sn) n-type thermoelectric alloys with proven maximum thermoelectric figure of merit ZT of 1.3. This success is based on combination of two approaches to maximize the thermoelectric performance: the band structure engineering and the alloying. In this chapter, we review data on crystal and electronic structure as well as on the thermoelectric properties of Mg2X compounds and their solid solutions
Theory of AC Josepson Effect in Superconducting Constrictions
We have developed a microscopic theory of ac Josephson effect in short
ballistic superconducting constrictions with arbitrary electron transparency
and in constrictions with diffusive electron transport. The theory is valid for
arbitrary miscroscopic structure of the superconducting electrodes of the
constriction. As applications of the theory we study smearing of the subgap
current singularities by pair-breaking effects and also the structure of these
singularities in the constrictions between the composite S/N electrodes with
the proximity-induced gap in the normal layer.Comment: 11 pages, RevTex, 3 figures available on reques
Josephson effect in superconducting constrictions with hybrid SF electrodes: peculiar properties determined by the misorientation of magnetizations
Josephson current in SFcFS junctions with arbitrary transparency of the
constriction (c) is investigated. The emphasis is done on the analysis of the
supercurrent dependencies on the misorientation angle between the
in-plane magnetizations of diffusive ferromagnetic layers (F). It is found that
the current-phase relation may be radically modified with the variation: the harmonic vanishes for definite value of
provided for identical orientation of the magnetizations () the junction is in the state. The Josephson current may exhibit a
nonmonotonic dependence on the misorientation angle both for realization of and state at . We also analyze the effect of exchange
field induced enhancement of the critical current which may occur in definite
range of .Comment: 7 pages, 5 figures, submitted to JETP Letter
Strong-Pinning Effects in Low-Temperature Creep: Charge-Density Waves in TaS_3
Nonlinear conduction in the quasi-one dimensional conductor o-TaS_3 has been
studied in the low-temperature region down to 30 mK. It was found that at
temperatures below a few Kelvins the current-voltage (I-V) characteristics
consist of several branches. The temperature evolution of the I-V curve
proceeds through sequential freezing-out of the branches. The origin of each
branch is attributed to a particular strong pinning impurity type.
Similar behavior is expected for other physical systems with collective
transport (spin-density waves, Wigner crystals, vortex lattices in type-II
superconductors etc.) in the presence of strong pinning centers.Comment: 11 pages, 3 ps figures, Revtex, To be published in Phys. Rev. Letters
(1997
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