11,246 research outputs found
Non local Andreev reflection in a carbon nanotube superconducting quantum interference device
We investigate a superconducting quantum interference device (SQUID) based on
carbon nanotubes in a fork geometry [J.-P. Cleuziou {\it et al.}, Nature
Nanotechnology {\bf 1}, 53 (2006)], involving tunneling of evanescent
quasiparticles through a superconductor over a distance comparable to the
superconducting coherence length, with therefore ``non local'' processes
generalizing non local Andreev reflection and elastic cotunneling. Non local
processes induce a reduction of the critical current and modify the
current-phase relation. We discuss arbitrary interface transparencies. Such
devices in fork geometries are candidates for probing the phase coherence of
crossed Andreev reflection.Comment: 13 pages, 8 figures, revised versio
Magnetoconductance of carbon nanotube p-n junctions
The magnetoconductance of p-n junctions formed in clean single wall carbon
nanotubes is studied in the noninteracting electron approximation and
perturbatively in electron-electron interaction, in the geometry where a
magnetic field is along the tube axis. For long junctions the low temperature
magnetoconductance is anomalously large: the relative change in the conductance
becomes of order unity even when the flux through the tube is much smaller than
the flux quantum. The magnetoconductance is negative for metallic tubes. For
semiconducting and small gap tubes the magnetoconductance is nonmonotonic;
positive at small and negative at large fields.Comment: 5 pages, 2 figure
Growth of solid hcp \^4He off the melting curve
We report studies of the growth of solid hcp \4he at pressures higher than
the bulk freezing pressure using a cell design that allows us to inject atoms
into the solid. Near the melting curve during injection we observe random
events during which the pressure recorded in the cell drops abruptly. These
events are accompanied by transient increases in the temperature of the cell.
We discuss these transients and conclude that they represent the solidification
of meta-stable liquid regions and the associated relief of strain in the local
solid. We also observe that further from the melting curve the transients are
no longer recorded, but that we can continue to add atoms to the solid,
increasing its density at fixed volume. We document these changes in density
with respect to changes in the chemical potential as a function of temperature
and discuss these in the context of recent theoretical work.Comment: 7 pages, 8 figure
Spin resolved Andreev reflection in ferromagnet-superconductor junctions with Zeeman splitting
Andreev reflection in ferromagnet-superconductor junctions is derived in a
regime in which Zeeman splitting dominates the response of the superconductor
to an applied magnetic field. Spin-up and spin-down Andreev reflections are
shown to be resolved as voltage is increased. In the metallic limit, the
transition from Andreev to tunnel conductivity in the spin-up channels has a
non trivial behavior when spin polarization is increased. The conductance is
asymmetric in a voltage reversal.Comment: RevTex. 13 pages. 3 figures include
On the spectrum of facet crystallization waves at the smooth 4He crystal surface
The wavelike processes of crystallization and melting or crystallization
waves are well known to exist at the 4He crystal surface in the rough state.
Much less is known about crystallization waves for the 4He crystal surface in
the smooth well-faceted state below the roughening transition temperature. To
meet the lack, we analyze here the spectrum of facet crystallization waves and
its dependence upon the wavelength, perturbation amplitude, and the number of
possible facet steps distributed somehow over the wavelength. All the
distinctive features of facet crystallization waves from conventional waves at
the rough surface result from a nonanalytic cusplike behavior in the angle
dependence for the surface tension of smooth crystal facets.Comment: 7 pages, 3 figures, 1 tabl
Mass flow through solid 4He induced by the fountain effect
Using an apparatus that allows superfluid liquid 4He to be in contact with
hcp solid \4he at pressures greater than the bulk melting pressure of the
solid, we have performed experiments that show evidence for 4He mass flux
through the solid and the likely presence of superfluid inside the solid. We
present results that show that a thermomechanical equilibrium in quantitative
agreement with the fountain effect exists between two liquid reservoirs
connected to each other through two superfluid-filled Vycor rods in series with
a chamber filled with solid 4He. We use the thermomechanical effect to induce
flow through the solid and measure the flow rate. On cooling, mass flux appears
near T = 600 mK and rises smoothly as the temperature is lowered. Near T = 75
mK a sharp drop in the flux is present. The flux increases as the temperature
is reduced below 75 mK. We comment on possible causes of this flux minimum.Comment: 20 pages, 22 figures, 7 table
Three Brane Action and The Correspondence Between N=4 Yang Mills Theory and Anti De Sitter Space
Recently, a relation between N=4 Super Yang Mills in 3+1 dimensions and
supergravity in an background has been proposed. In this paper we
explore the idea that the correspondence between operators in the Yang Mills
theory and modes of the supergravity theory can be obtained by using the D3
brane action. Specifically, we consider two form gauge fields for this purpose.
The supergravity analysis predicts that the operator which corresponds to this
mode has dimension six. We show that this is indeed the leading operator in the
three brane Dirac-Born-Infeld and Wess-Zumino action which couples to this
mode. It is important in the analysis that the brane action is expanded around
the anti de-Sitter background. Also, the Wess-Zumino term plays a crucial role
in cancelling a lower dimension operator which appears in the the
Dirac-Born-Infeld action.Comment: 12 pages, LaTex, no figures; error in the form of the final dimension
six operator corrected, some references and comments added, main conclusions
unchange
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
Two-photon correlations as a sign of sharp transition in quark-gluon plasma
The photon production arising due to time variation of the medium has been
considered. The Hamilton formalism for photons in time-variable medium (plasma)
has been developed with application to inclusive photon production. The results
have been used for calculation of the photon production in the course of
transition from quark-gluon phase to hadronic phase in relativistic heavy ion
collisions. The relative strength of the effect as well as specific two- photon
correlations have been evaluated. It has been demonstrated that the opposite
side two-photon correlations are indicative of the sharp transition from the
quark-gluon phase to hadrons.Comment: 23 pages, 2 figure
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