695 research outputs found
Josephson junctions in thin and narrow rectangular superconducting strips
I consider a Josephson junction crossing the middle of a thin rectangular
superconducting strip of length L and width W subjected to a perpendicular
magnetic induction B. I calculate the spatial dependence of the gauge-invariant
phase difference across the junction and the resulting B dependence of the
critical current Ic(B).Comment: 4 pages, 6 figures, revised following referee's comment
Spin-Valve Effect of the Spin Accumulation Resistance in a Double Ferromagnet - Superconductor Junction
We have measured the transport properties of Ferromagnet - Superconductor
nanostructures, where two superconducting aluminum (Al) electrodes are
connected through two ferromagnetic iron (Fe) ellipsoids in parallel. We find
that, below the superconducting critical temperature of Al, the resistance
depends on the relative alignment of the ferromagnets' magnetization. This
spin-valve effect is analyzed in terms of spin accumulation in the
superconducting electrode submitted to inverse proximity effect
The Ginzburg-Landau theory in application
A numerical approach to Ginzburg-Landau (GL) theory is demonstrated and we
review its applications to several examples of current interest in the research
on superconductivity. This analysis also shows the applicability of the
two-dimensional approach to thin superconductors and the re-defined effective
GL parameter kappa. For two-gap superconductors, the conveniently written GL
equations directly show that the magnetic behavior of the sample depends not
just on the GL parameter of two bands, but also on the ratio of respective
coherence lengths.Comment: To be published in Physica C, VORTEX VI Conference Proceeding
Geometry-dependent critical currents in superconducting nanocircuits
In this paper we calculate the critical currents in thin superconducting
strips with sharp right-angle turns, 180-degree turnarounds, and more
complicated geometries, where all the line widths are much smaller than the
Pearl length . We define the critical current as the
current that reduces the Gibbs free-energy barrier to zero. We show that
current crowding, which occurs whenever the current rounds a sharp turn, tends
to reduce the critical current, but we also show that when the radius of
curvature is less than the coherence length this effect is partially
compensated by a radius-of-curvature effect. We propose several patterns with
rounded corners to avoid critical-current reduction due to current crowding.
These results are relevant to superconducting nanowire single-photon detectors,
where they suggest a means of improving the bias conditions and reducing dark
counts. These results also have relevance to normal-metal nanocircuits, as
these patterns can reduce the electrical resistance, electromigration, and hot
spots caused by nonuniform heating.Comment: 29 pages, 24 figure
Phase transition curves for mesoscopic superconducting samples
We compute the phase transition curves for mesoscopic superconductors.
Special emphasis is given to the limiting shape of the curve when the magnetic
flux is large. We derive an asymptotic formula for the ground state of the
Schr\"odinger equation in the presence of large applied flux. The expansion is
shown to be sensitive to the smoothness of the domain. The theoretical results
are compared to recent experiments.Comment: 8 pages, 1 figur
H_c_3 for a thin-film superconductor with a ferromagnetic dot
We investigate the effect of a ferromagnetic dot on a thin-film
superconductor. We use a real-space method to solve the linearized
Ginzburg-Landau equation in order to find the upper critical field, H_c_3. We
show that H_c_3 is crucially dependent on dot composition and geometry, and may
be significantly greater than H_c_2. H_c_3 is maximally enhanced when (1) the
dot saturation magnetization is large, (2) the ratio of dot thickness to dot
diameter is of order one, and (3) the dot thickness is large
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