432 research outputs found
Andreev Reflection and Proximity effect
The Andreev Reflection is the key mechanism for the superconducting proximity
effect. It provides phase correlations in a system of non-interacting electrons
at mesoscopic scales, i.e. over distances much larger than the microscopic
lengths : Fermi wavelength and elastic electron mean free path. This field of
research has attracted an increasing interest in the recent years in part
because of the tremendous development of nanofabrication technologies, and also
because of the richness of the involved quantum effects. In this paper we
review some recently achieved advances. We also discuss new open questions, in
particular non-equilibrium effects and proximity effect in systems with
ferromagnetic elements.Comment: 17 pages, no figure, to appear in J. of Low Temp. Phys., proceeding
of the LT satellite conference "Electron Transport in Mesoscopic Systems",
reference list correcte
Charge density wave transport in submicron antidot arrays in NbSe3
We demonstrate for the first time that a periodic array of submicrometer
holes (antidots) can be patterned into thin single NbSe3 crystals. We report on
the study of charge density wave (CDW) transport of the network of mesoscopic
units between antidots. Size of the elementary unit can be as small as 0.5
micron along the chain axis and (0.2 micron) x (0.3 micron) in cross section.
We observe size effects for Ohmic residual resistance and in CDW transport
current-voltage characteristics in submicronic networks.Comment: 4 pages with 1 table and 10 figures. Submitted to European Physical
Journa
Mesoscopic transition in the shot noise of diffusive S/N/S junctions
We experimentally investigated the current noise in diffusive
Superconductor/Normal metal/Superconductor junctions with lengths between the
superconducting coherence length xi_Delta and the phase coherence length L_Phi
of the normal metal (xi_Delta < L < L_Phi). We measured the shot noise over a
large range of energy covering both the regimes of coherent and incoherent
multiple Andreev reflections. The transition between these two regimes occurs
at the Thouless energy where a pronounced minimum in the current noise density
is observed. Above the Thouless energy, in the regime of incoherent multiple
Andreev reflections, the noise is strongly enhanced compared to a normal
junction and grows linearly with the bias voltage. Semi-classical theory
describes the experimental results accurately, when taking into account the
voltage dependence of the resistance which reflects the proximity effect. Below
the Thouless energy, the shot noise diverges with decreasing voltage which may
indicate the coherent transfer of multiple charges.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. B, Rapid
Communicatio
Local spectroscopy of a proximity superconductor at very low temperature
We performed the local spectroscopy of a Normal-metal--Superconductor (N-S)
junction with the help of a very low temperature (60 mK) Scanning Tunneling
Microscope (STM). The spatial dependence of the local density of states was
probed locally in the vicinity of the N-S interface. We observed spectra with a
fully-developed gap in the regions where a thin normal metal layer caps the
superconductor dot. Close to the S metal edge, a clear pseudo-gap shows up,
which is characteristic of the superconducting proximity effect in the case of
a long normal metal. The experimental results are compared to the predictions
of the quasiclassical theory.Comment: 7 pages, 3 figure
Measurement of the Current-Phase Relation in Josephson Junctions Rhombi Chains
We present low temperature transport measurements in one dimensional
Josephson junctions rhombi chains. We have measured the current phase relation
of a chain of 8 rhombi. The junctions are either in the classical phase regime
with the Josephson energy much larger than the charging energy, , or in the quantum phase regime where . In the
strong Josephson coupling regime () we observe a
sawtooth-like supercurrent as a function of the phase difference over the
chain. The period of the supercurrent oscillations changes abruptly from one
flux quantum to half the flux quantum as the rhombi are
tuned in the vicinity of full frustration. The main observed features can be
understood from the complex energy ground state of the chain. For
we do observe a dramatic suppression and rounding of the
switching current dependence which we found to be consistent with the model
developed by Matveev et al.(Phys. Rev. Lett. {\bf 89}, 096802(2002)) for long
Josephson junctions chains.Comment: to appear in Phys. Rev.
Localization Effect in a 2D Superconducting Network without Disorder
The superconducting properties of a two-dimensional superconducting wire
network with a new geometry have been measured as a function of the external
magnetic field. The extreme localization effect recently predicted for this
periodic lattice is revealed as a suppression of the critical current when the
applied magnetic field corresponds to half a flux quantum per unit cell. For
this particular magnetic field, the observed vortex state configuration is
highly disordered.Comment: 6 pages, 2 eps figures, submitted to Physica C. Title change
The Josephson critical current in a long mesoscopic S-N-S junction
We carry out an extensive experimental and theoretical study of the Josephson
effect in S-N-S junctions made of a diffusive normal metal (N) embedded between
two superconducting electrodes (S). Our experiments are performed on Nb-Cu-Nb
junctions with highly-transparent interfaces. We give the predictions of the
quasiclassical theory in various regimes on a precise and quantitative level.
We describe the crossover between the short and the long junction regimes and
provide the temperature dependence of the critical current using dimensionless
units and where
is the Thouless energy. Experimental and theoretical results are in excellent
quantitative agreement.Comment: 5 pages, 4 figures, slighly modified version, publishe
A very low temperature STM for the local spectroscopy of mesoscopic structures
We present the design and operation of a very-low temperature Scanning
Tunneling Microscope (STM) working at in a dilution refrigerator. The
STM features both atomic resolution and micron-sized scanning range at low
temperature. This work is the first experimental realization of a local
spectroscopy of mesoscopic structures at very low temperature. We present
high-resolution current-voltage characteristics of tunnel contacts and the
deduced local density of states of hybrid Superconductor-Normal metal systems.Comment: 5 pages, 5 figures, slightly corrected versio
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