19,910 research outputs found
Crossed conductance in FSF double junctions: role of out-of-equilibrium populations
We discuss a model of Ferromagnet / Superconductor / Ferromagnet (FSF) double
junction in which the quasiparticles are not in equilibrium with the condensate
in a region of the superconductor containing the two FS contacts. The role of
geometry is discussed, as well as the role of a small residual density of
states within the superconducting gap, that allows a sequential tunneling
crossed current. With elastic quasiparticle transport and the geometry with
lateral contacts, the crossed conductances in the sequential tunneling channel
are almost equal in the normal and superconducting phases, if the distance
between the FS interfaces is sufficiently small. The sequential tunneling and
spatially separated processes (the so-called crossed Andreev reflection and
elastic cotunneling processes) lead to different signs of the crossed current
in the antiparallel alignment for tunnel interfaces.Comment: 8 pages, 4 figure
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Numerical Simulation of Baroclinic Jovian Vortices
We examine the evolution of baroclinic vortices in a time-dependent, nonlinear numerical model of a Jovian atmosphere. The model uses a normal-mode expansion in the vertical, using the barotropic and first two baroclinic modes. Results for the stability of baroclinic vortices on an f plane in the absence of a mean zonal flow are similar to results of Earth vortex models, although the presence of a fluid interior on the Jovian planets shifts the stability boundaries to smaller length scales. The presence of a barotropic mean zonal flow in the interior stabilizes vortices against instability and significantly modifies the finite amplitude form of baroclinic instabilities. The effect of a zonal flow on a form of barotropic instability produces periodic oscillations in the latitude and longitude of the vortex as observed at the level of the cloud tops. This instability may explain some, but not all, observations of longitudinal oscillations of vortices on the outer planets. Oscillations in aspect ratio and orientation of stable vortices in a zonal shear flow are observed in this baroclinic model, as in simpler twodimensional models. Such oscillations are also observed in the atmospheres of Jupiter and Neptune. The meridional propagation and decay of vortices on a β plane is inhibited by the presence of a mean zonal flow. The direction of propagation of a vortex relative to the mean zonal flow depends upon the sign of the meridional potential vorticity gradient; combined with observations of vortex drift rates, this may provide a constraint on model assumption for the flow in the deep interior of the Jovian planets
Contribution of weak localization to non local transport at normal metal / superconductor double interfaces
In connection with a recent experiment [Russo {\it et al.}, Phys. Rev. Lett.
{\bf 95}, 027002 (2005)], we investigate the effect of weak localization on non
local transport in normal metal / insulator / superconductor / insulator /
normal metal (NISIN) trilayers, with extended interfaces. The negative weak
localization contribution to the crossed resistance can exceed in absolute
value the positive elastic cotunneling contribution if the normal metal phase
coherence length or the energy are large enough.Comment: 9 pages, 7 figures, minor modification
5D Yang-Mills instantons from ABJM Monopoles
In the presence of a background supergravity flux, N M2-branes will expand
via the Myers effect into M5-branes wrapped on a fuzzy three-sphere. In
previous work the fluctuations of the M2-branes were shown to be described by
the five-dimensional Yang-Mills gauge theory associated to D4-branes. We show
that the ABJM prescription for eleven-dimensional momentum in terms of magnetic
flux lifts to an instanton flux of the effective five-dimensional Yang-Mills
theory on the sphere, giving an M-theory interpretation for these instantons.Comment: 29 pages, Latex; v2: added references and a comment on the
graviphoton coupling in section 5; v3: typos corrected and references adde
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