4,728 research outputs found
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
ac Josephson effect in asymmetric superconducting quantum point contacts
We investigate ac Josephson effects between two superconductors connected by
a single-mode quantum point contact, where the gap amplitudes in the two
superconductors are unequal. In these systems, it was found in previous studies
on the dc effects that, besides the Andreev bound-states, the continuum states
can also contribute to the current. Using the quasiclassical formulation, we
calculate the current-voltage characteristics for general transmission of
the point contact. To emphasize bound versus continuum states, we examine in
detail the low bias, ballistic (D=1) limit. It is shown that in this limit the
current-voltage characteristics can be determined from the current-phase
relation, if we pay particular attention to the different behaviors of these
states under the bias voltage. For unequal gap configurations, the continuum
states give rise to non-zero sine components. We also demonstrate that in this
limit the temperature dependence of the dc component follows
, where is the smaller gap, with the
contribution coming entirely from the bound state.Comment: To appear in PR
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
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
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
Depinning transition of dislocation assemblies: pileup and low-angle grain boundary
We investigate the depinning transition occurring in dislocation assemblies.
In particular, we consider the cases of regularly spaced pileups and low angle
grain boundaries interacting with a disordered stress landscape provided by
solute atoms, or by other immobile dislocations present in non-active slip
systems. Using linear elasticity, we compute the stress originated by small
deformations of these assemblies and the corresponding energy cost in two and
three dimensions. Contrary to the case of isolated dislocation lines, which are
usually approximated as elastic strings with an effective line tension, the
deformations of a dislocation assembly cannot be described by local elastic
interactions with a constant tension or stiffness. A nonlocal elastic kernel
results as a consequence of long range interactions between dislocations. In
light of this result, we revise statistical depinning theories and find novel
results for Zener pinning in grain growth. Finally, we discuss the scaling
properties of the dynamics of dislocation assemblies and compare theoretical
results with numerical simulations.Comment: 13 pages, 8 figure
Depinning transition of dislocation assemblies: pileup and low-angle grain boundary
We investigate the depinning transition occurring in dislocation assemblies.
In particular, we consider the cases of regularly spaced pileups and low angle
grain boundaries interacting with a disordered stress landscape provided by
solute atoms, or by other immobile dislocations present in non-active slip
systems. Using linear elasticity, we compute the stress originated by small
deformations of these assemblies and the corresponding energy cost in two and
three dimensions. Contrary to the case of isolated dislocation lines, which are
usually approximated as elastic strings with an effective line tension, the
deformations of a dislocation assembly cannot be described by local elastic
interactions with a constant tension or stiffness. A nonlocal elastic kernel
results as a consequence of long range interactions between dislocations. In
light of this result, we revise statistical depinning theories and find novel
results for Zener pinning in grain growth. Finally, we discuss the scaling
properties of the dynamics of dislocation assemblies and compare theoretical
results with numerical simulations.Comment: 13 pages, 8 figure
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
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
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