152 research outputs found
Probing interfacial pair breaking in tunnel junctions based on the first and the second harmonics of the Josephson current
It will be shown that a pronounced interfacial pair breaking can be
identified in Josephson tunnel junctions provided the first j_{1c} and the
second j_{2c} harmonics of the supercurrent, as well as the depairing current
in the bulk j_{dp}, are known. Namely, within the Ginzburg-Landau theory a
strong interfacial pair breaking results in the relation
j_{2c}j_{dp}>>j_{1c}^2, while in standard junctions, with negligibly small pair
breaking, the relation of opposite character takes place.Comment: 6 pages, published versio
Calculation of gluon and four-quark condensates from the operator expansion
The magnitudes of gluon and four-quark condensates are found from the
analysis of vector mesons consisting of light quarks (the families of
and mesons) in the 3 loops approximation. The QCD model with infinite
number of vector mesons is used to describe the function . This model
describes well the experimental function . Polarization operators
calculated with this model coincide with the Wilson operator expansion at large
. The improved perturbative theory, such that the polarization operators
have correct analytical properties, is used. The result is . The electronic widths of and
are calculated.Comment: 18 pages, latex, changed content slightl
Dissociation of vortex stacks into fractional-flux vortices
We discuss the zero field superconducting phase transition in a finite system
of magnetically coupled superconducting layers. Transverse screening is
modified by the presence of other layers resulting in topological excitations
with fractional flux. Vortex stacks trapping a full flux and present at any
finite temperature undergo an evaporation transition which corresponds to the
depairing of fractional-flux vortices in individual layers. We propose an
experiment with a bi-layer system allowing us to identify the dissociation of
bound vortex molecules.Comment: 4 pages, 1 figure; revised version, to appear in Phys. Rev. Let
Theory of the Resistive Transition in Overdoped : Implications for the angular dependence of the quasiparticle scattering rate in High- superconductors
We show that recent measurements of the magnetic field dependence of the
magnetization, specific heat and resistivity of overdoped
in the vicinity of the superconducting
imply that the vortex viscosity is anomalously small and that the material
studied is inhomogeneous with small, a few hundred , regions in which the
local is much higher than the bulk . The anomalously small
vortex viscosity can be derived from a microscopic model in which the
quasiparticle lifetime varies dramatically around the Fermi surface, being
small everywhere except along the zone diagonal (``cold spot''). We propose
experimental tests of our results.Comment: 4 pages, LaTex, 2 EPS figure
Correlator of Topological Charge Densities in Instanton Model in QCD
The QCD sum rule for the correlator of topological charge densities and
related to it longitudinal part of the correlator of singlet axial currents is
considered in the framework of instanton model. The coupling constant of
eta'-meson with the singlet axial current is determined. Its value appears to
be in a good coincidence with the value determined recently from the connection
of the part of proton spin, carried by u,d,s quarks, with the derivative of QCD
topological susceptibility. From the same sum rule eta-eta' mixing angle is
found in the framework of two mixing angles model. Its value is close to that
found in the chiral effective theory. The correlator of topological charge
densities at large momenta is calculated.Comment: 14 pages, 2 figure
Free-energy distribution functions for the randomly forced directed polymer
We study the -dimensional random directed polymer problem, i.e., an
elastic string subject to a Gaussian random potential and
confined within a plane. We mainly concentrate on the short-scale and
finite-temperature behavior of this problem described by a short- but
finite-ranged disorder correlator and introduce two types of
approximations amenable to exact solutions. Expanding the disorder potential
at short distances, we study the
random force (or Larkin) problem with as well as the shifted
random force problem including the random offset ; as such, these
models remain well defined at all scales. Alternatively, we analyze the
harmonic approximation to the correlator in a consistent manner.
Using direct averaging as well as the replica technique, we derive the
distribution functions and of free energies
of a polymer of length for both fixed () and free boundary
conditions on the displacement field and determine the mean
displacement correlators on the distance . The inconsistencies encountered
in the analysis of the harmonic approximation to the correlator are traced back
to its non-spectral correlator; we discuss how to implement this approximation
in a proper way and present a general criterion for physically admissible
disorder correlators .Comment: 16 pages, 5 figure
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