5,876 research outputs found
Proximity Effect Enhancement Induced by Roughness of SN Interface
Critical temperature reduction is considered for a thin film of
a layered superconductor (S) with a rough surface covered by a thick layer of a
normal metal (N). The roughness of the SN interface increases the penetration
of electrons from the normal metal into the superconductor and leads to an
enhancement of the proximity effect. The value of induced by the
roughness of the SN interface can be much higher than for a film
with a plain surface for an extremely anisotropic layered superconductor with
the coherence lengths .Comment: 2 page
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
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
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
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
NN potentials from inverse scattering in the J-matrix approach
An approximate inverse scattering method [7,8] has been used to construct
separable potentials with the Laguerre form factors. As an application, we
invert the phase shifts of proton-proton in the and
channels and neutron-proton in the channel elastic scattering. In
the latter case the deuteron wave function of a realistic potential was
used as input.Comment: LaTex2e, 17 pages, 3 Postscript figures; corrected typo
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
Shadow on the wall cast by an Abrikosov vortex
At the surface of a d-wave superconductor, a zero-energy peak in the
quasiparticle spectrum can be observed. This peak appears due to Andreev bound
states and is maximal if the nodal direction of the d-wave pairing potential is
perpendicular to the boundary. We examine the effect of a single Abrikosov
vortex in front of a reflecting boundary on the zero-energy density of states.
We can clearly see a splitting of the low-energy peak and therefore a
suppression of the zero-energy density of states in a shadow-like region
extending from the vortex to the boundary. This effect is stable for different
models of the single Abrikosov vortex, for different mean free paths and also
for different distances between the vortex center and the boundary. This
observation promises to have also a substantial influence on the differential
conductance and the tunneling characteristics for low excitation energies.Comment: 5 pages, 5 figure
Non-local electron transport and cross-resistance peak in NSN heterostructures
We develop a microscopic theory describing the peak in the temperature
dependence of the non-local resistance of three-terminal NSN devices. This peak
emerges at sufficiently high temperatures as a result of a competition between
quasiparticle/charge imbalance and subgap (Andreev) contributions to the
conductance matrix. Both the height and the shape of this peak demonstrate the
power law dependence on the superconductor thickness in contrast to the
zero-temperature non-local resistance which decays (roughly) exponentially with
increasing . A similar behavior was observed in recent experiments.Comment: 4 pages, 3 figure
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
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