4,720 research outputs found
Quantitative Simulation of the Superconducting Proximity Effect
A numerical method is developed to calculate the transition temperature of
double or multi-layers consisting of films of super- and normal conductors. The
approach is based on a dynamic interpretation of Gorkov's linear gap equation
and is very flexible. The mean free path of the different metals, transmission
through the interface, ratio of specular reflection to diffusive scattering at
the surfaces, and fraction of diffusive scattering at the interface can be
included. Furthermore it is possible to vary the mean free path and the BCS
interaction NV in the vicinity of the interface. The numerical results show
that the normalized initial slope of an SN double layer is independent of
almost all film parameters except the ratio of the density of states. There are
only very few experimental investigations of this initial slope and they
consist of Pb/Nn double layers (Nn stands for a normal metal). Surprisingly the
coefficient of the initial slope in these experiments is of the order or less
than 2 while the (weak coupling) theory predicts a value of about 4.5. This
discrepancy has not been recognized in the past. The autor suggests that it is
due to strong coupling behavior of Pb in the double layers. The strong coupling
gap equation is evaluated in the thin film limit and yields the value of 1.6
for the coefficient. This agrees much better with the few experimental results
that are available.
PACS: 74.45.+r, 74.62.-c, 74.20.F
Andreev bound states and tunneling characteristics of a non-centrosymmetric superconductor
The tunneling characteristics of planar junctions between a normal metal and
a non-centrosymmetric superconductor like CePt3Si are examined. It is shown
that the superconducting phase with mixed parity can give rise to
characteristic zero-bias anomalies in certain junction directions. The origin
of these zero-bias anomalies are Andreev bound states at the interface. The
tunneling characteristics for different directions allow to test the structure
of the parity-mixed pairing state.Comment: 4 pages, 3 figure
Circuit theory of unconventional superconductor junctions
We extend the circuit theory of superconductivity to cover transport and
proximity effect in mesoscopic systems that contain unconventional
superconductor junctions. The approach fully accounts for zero-energy Andreev
bound states forming at the surface of unconventional superconductors. As a
simple application, we investigate the transport properties of a diffusive
normal metal in series with a d-wave superconductor junction. We reveal the
competition between the formation of Andreev bound states and proximity effect,
that depends on the crystal orientation of the junction interface.Comment: 4 page
Proximity Effect in Normal Metal - High Tc Superconductor Contacts
We study the proximity effect in good contacts between normal metals and high
Tc (d-wave) superconductors. We present theoretical results for the spatially
dependent order parameter and local density of states, including effects of
impurity scattering in the two sides, s-wave pairing interaction in the normal
metal side (attractive or repulsive), as well as subdominant s-wave paring in
the superconductor side. For the [100] orientation, a real combination d+s of
the order parameters is always found. The spectral signatures of the proximity
effect in the normal metal includes a suppression of the low-energy density of
states and a finite energy peak structure. These features are mainly due to the
impurity self-energies, which dominate over the effects of induced pair
potentials. For the [110] orientation, for moderate transparencies, induction
of a d+is order parameter on the superconductor side, leads to a proximity
induced is order parameter also in the normal metal. The spectral signatures of
this type of proximity effect are potentially useful for probing time-reversal
symmetry breaking at a [110] interface.Comment: 10 pages, 10 figure
Collective Dynamics of One-Dimensional Charge Density Waves
The effect of disorder on the static and dynamic behaviour of one-dimensional
charge density waves at low temperatures is studied by analytical and numerical
approaches. In the low temperature region the spatial behaviour of the
phase-phase correlation function is dominated by disorder but the roughness
exponent remains the same as in the pure case. Contrary to high dimensional
systems the dependence of the creep velocity on the electric field is described
by an analytic function.Comment: 4 pages, 4 figure
Severe discrepancies between experiment and theory in the superconducting proximity effect
The superconducting proximity effect is investigated for SN double layers in
a regime where the resulting transition temperature T_{c} does not depend on
the mean free paths of the films and, within limits, not on the transparency of
the interface. This regime includes the thin film limit and the normalized
initial slope S_{sn}= (d_{s}/T_{s})|dT_{c}/dd_{n}|. The experimental results
for T_{c} are compared with a numerical simulation which was recently developed
in our group. The results for the SN double layers can be devided into three
groups: (i) When N = Cu, Ag, Au, Mg a disagreement between experiment and
theory by a factor of the order of three is observed, (ii) When N = Cd, Zn, Al
the disagreement between experiment and theory is reduced to a factor of about
1.5, (iii) When N = In, Sn a reasonably good agreement between experiment and
theory is observed
Projection on Segre varieties and determination of holomorphic mappings between real submanifolds
It is shown that a germ of a holomorphic mapping sending a real-analytic
generic submanifold of finite type into another is determined by its projection
on the Segre variety of the target manifold. A necessary and sufficient
condition is given for a germ of a mapping into the Segre variety of the target
manifold to be the projection of a holomorphic mapping sending the source
manifold into the target. An application to the biholomorphic equivalence
problem is also given.Comment: 16 page
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
Andreev experiments on superconductor/ferromagnet point contacts
Andreev reflection is a smart tool to investigate the spin polarisation P of
the current through point contacts between a superconductor and a ferromagnet.
We compare different models to extract P from experimental data and investigate
the dependence of P on different contact parameters.Comment: 14 pages, 5 figures, accepted for publication in Fizika Nizkikh
Temperatu
Observation of the second harmonic in superconducting current-phase relation of Nb/Au/(001)YBa2Cu3Ox heterojunctions
The superconducting current-phase relation (CPR) of Nb/Au/(001)YBa2Cu3Ox
heterojunctions prepared on epitaxial c-axis oriented YBa2Cu3Ox thin films has
been measured in a single-junction interferometer. For the first time, the
second harmonic of the CPR of such junctions has been observed. The appearance
of the second harmonic and the relative sign of the first and second harmonics
of the CPR can be explained assuming, that the macroscopic pairing symmetry of
our YBa2Cu3Ox thin films is of the d+s typeComment: 11 pages, 4 figure
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