380 research outputs found
Influence of the temperature on the depinning transition of driven interfaces
We study the dynamics of a driven interface in a two-dimensional random-field
Ising model close to the depinning transition at small but finite temperatures
T using Glauber dynamics. A square lattice is considered with an interface
initially in (11)-direction. The drift velocity v is analyzed for the first
time using finite size scaling at T = 0 and additionally finite temperature
scaling close to the depinning transition. In both cases a perfect data
collapse is obtained from which we deduce beta = 1/3 for the exponent which
determines the dependence of v on the driving field, nu = 1 for the exponent of
the correlation length and delta = 5 for the exponent which determines the
dependence of v on T.Comment: 5 pages, Latex, Figures included, to appear in Europhys. Let
Modelling the energy gap in transition metal/aluminium bilayers"
We present an application of the generalised proximity effect theory.Comment: 15 pages, 11 figures, presented at workshop on low temperature
superconducting electronics at the University of Twente, The Netherland
Supercurrent in a mesoscopic proximity wire
Recent experiments on the proximity induced supercurrent in mesoscopic normal
wires revealed a surprising temperature dependence. They suggest clean-limit
behavior although the wires are strongly disordered. We demonstrate that this
unexpected scaling is actually contained in the conventional description of
diffusive superconductors and find excellent agreement with the experimental
results. In addition we propose a SQUID-like proximity structure for further
experimental investigations of the effects in question.Comment: 6 pages LaTeX, 4 postscript figures; to appear in J. Low Temp. Phys.
(Proceedings of WSS '96
Magnetic breakdown in a normal-metal - superconductor proximity sandwich
We study the magnetic response of a clean normal-metal slab of finite
thickness in proximity with a bulk superconductor. We determine its free energy
and identify two (meta-)stable states, a diamagnetic one where the applied
field is effectively screened, and a second state, where the field penetrates
the normal-metal layer. We present a complete characterization of the first
order transition between the two states which occurs at the breakdown field,
including its spinodals, the jump in the magnetization, and the latent heat.
The bistable regime terminates at a critical temperature above which the sharp
transition is replaced by a continuous cross-over. We compare the theory with
experiments on normal-superconducting cylinders.Comment: 7 pages Revtex, 3 Postscript figures, needs psfig.te
Density of States and Energy Gap in Andreev Billiards
We present numerical results for the local density of states in semiclassical
Andreev billiards. We show that the energy gap near the Fermi energy develops
in a chaotic billiard. Using the same method no gap is found in similar square
and circular billiards.Comment: 9 pages, 6 Postscript figure
Superconductive properties of thin dirty SN bilayers
The theory of superconductivity in thin SN sandwiches (bilayers) in the
diffusive limit is developed within the standard Usadel equation method, with
particular emphasis on the case of very thin superconductive layers, d_S <<
d_N. The proximity effect in the system is governed by the interlayer interface
resistance (per channel) \rho_{int}. The case of relatively low resistance
(which can still have large absolute values) can be completely studied
analytically. The theory describing the bilayer in this limit is of BCS type
but with the minigap (in the single-particle density of states) E_g << \Delta
substituting the order parameter \Delta in the standard BCS relations; the
original relations are thus severely violated. In the opposite limit of an
opaque interface, the behavior of the system is in many respects close to the
BCS predictions. Over the entire range of \rho_{int}, the properties of the
bilayer are found numerically. Finally, it is shown that the results obtained
for the bilayer also apply to more complicated structures such as SNS and NSN
trilayers, SNINS and NSISN systems, and SN superlattices.Comment: 15 pages (including 10 EPS figures), REVTeX. Version 2: minor
changes; added references, a note is added concerning applicability of our
results to SNINS and NSISN systems. To appear in Phys. Rev. B on March 1,
200
Anomalous proximity effect in d-wave superconductors
The anomalous proximity effect between a d-wave superconductor and a surface
layer with small electronic mean free path is studied theoretically in the
framework of the Eilenberger equations. The angular and spatial structure of
the pair potential and the quasiclassical propagators in the interface region
is calculated selfconsistently. The variation of the spatially-resolved
quasiparticle density of states from the bulk to the surface is studied. It is
shown that the isotropic gapless superconducting state is induced in the
disordered layer.Comment: 6 pages, 5 postscript figures. Submitted to Phys.Rev.
Domain wall superconductivity in superconductor/ferromagnet bilayers
We analyze the enhancement of the superconducting critical temperature of
superconducting/ferromagnetic bilayers due to the appearance of localized
superconducting states in the vicinity of magnetic domain walls in the
ferromagnet. We consider the case when the main mechanism of the
superconductivity destruction via the proximity effect is the exchange field.
We demonstrate that the influence of the domain walls on the superconducting
properties of the bilayer may be quite strong if the domain wall thickness is
of the order of superconducting coherence length.Comment: 8 pages, 2 figure
The current-phase relation in Josephson tunnel junctions
The relation in SFIFS, SNINS and SIS tunnel junctions is studied.
The method for analytical solution of linearized Usadel equations has been
developed and applied to these structures. It is shown that the Josephson
current across the structure has the sum of and
components. Two different physical mechanisms are responsible for the sign of
. The first one is the depairing by current which contributes
positively to the term, while the second one is the finite
transparency of SF or SN interfaces which provides the negative contribution.
In SFIFS junctions, where the first harmonic vanishes at 0 - transition,
the calculated second harmonic fully determines the curve.Comment: 6 pages, 2 figure
Cryptoferromagnetic state in superconductor-ferromagnet multilayers
We study a possibility of a non-homogeneous magnetic order
(cryptoferromagnetic state) in heterostructures consisting of a bulk
superconductor and a ferromagnetic thin layer that can be due to the influence
of the superconductor. The exchange field in the ferromagnet may be strong and
exceed the inverse mean free time. A new approach based on solving the
Eilenberger equations in the ferromagnet and the Usadel equations in the
superconductor is developed. We derive a phase diagram between the
cryptoferromagnetic and ferromagnetic states and discuss the possibility of an
experimental observation of the CF state in different materials.Comment: 4 pages, 1 figur
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