4,575 research outputs found
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
Nonmonotonic temperature dependence of critical current in diffusive d-wave junctions
We study the Josephson effect in D/I/DN/I/D junctions, where I, DN and D
denote an insulator, a diffusive normal metal and a d-wave superconductor,
respectively.The Josephson current is calculated based on the quasiclassical
Green's function theory with a general boundary condition for unconventional
superconducting junctions. In contrast to s-wave junctions, the product of the
Josephson current and the normal state resistance is enhanced by making the
interface barriers stronger. The Josephson current has a nonmonotonic
temperature dependence due to the competition between the proximity effect and
the midgap Andreev resonant states.Comment: 5 pages, 4 figure
Theory of thermal and charge transport in diffusive normal metal / superconductor junctions
Thermal and charge transport in the diffusive normal metal(DN) / insulator /
-, - and p-wave superconductor junctions are studied for various
situations, where we have used the Usadel equation with Nazarov's generalized
boundary condition. Thermal and electrical conductance of the junction and the
Lorentz ratio are calculated by varying the magnitudes of the resistance, the
Thouless energy and the magnetic scattering rate in DN, the transparency of the
insulating barrier, and the angle between the normal to the interface and the
crystal axis of d-wave superconductors or the angle between the normal to the
interface and the lobe direction of the p-wave pair potential. New general
expression is derived for the calculation of the thermal conductance. It is
demonstrated that the proximity effect doesn't influence the thermal
conductance while the mid gap Andreev resonant states suppress it. We have also
discussed a possibility of distinguishing pairing symmetries based on the
dependencies of the electrical and thermal conductance on temperatures.Comment: 21 pages, 20 figures, stylistic changes in v
Andreev reflection and enhanced subgap conductance in NbN/Au/InGaAs-InP junctions
We report on the fabrication of highly transparent superconductor/normal
metal/two-dimensional electron gas junctions formed by a superconducting NbN
electrode, a thin (10nm) Au interlayer, and a two-dimensional electron gas in a
InGaAs/InP heterostructure. High junction transparency has been achieved by
exploiting of a newly developed process of Au/NbN evaporation and rapid
annealing at 400C. This allowed us to observe for the first time a decrease in
the differential resistance with pronounced double-dip structure within the
superconducting energy gap in superconductor-2DEG proximity systems. The effect
of a magnetic field perpendicular to the plane of the 2DEG on the differential
resistance of the interface was studied. It has been found that the reduced
subgap resistance remains in high magnetic fields. Zero-field data are analyzed
within the previously established quasiclassical model for the proximity
effect.Comment: 15 pages, 5 figure
Non-Fraunhofer Interference Pattern in Inhomogeneous Ferromagnetic Josephson Junctions
Generic conditions are established for producing a non-Fraunhofer response of
the critical supercurrent subject to an external magnetic field in
ferromagnetic Josephson junctions. Employing the quasiclassical Keldysh-Usadel
method, we demonstrate theoretically that an inhomogeneity in the magnitude of
the energy scales in the system, including Thouless energy, exchange field and
temperature gradient normal to the transport direction, influences drastically
the standard Fraunhofer pattern. The exotic non-Fraunhofer response, similar to
that observed in recent experiments, is described in terms of an intricate
interplay between multiple '0-pi'-states and is related to the appearance of
proximity vortices.Comment: 5 pages, 3 figures. To Appear in Physical Review Letter
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
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