1,002 research outputs found
Superconducting and Magnetic Properties of Nb/Pd_1-xFe_x/Nb Triple Layers
The superconducting and magnetic properties of Nb/Pd_1-xFe_x/Nb triple layers
with constant Nb layer thickness d_Nb=200 A and different interlayer
thicknesses are investigated. The thickness dependence of the magnetization and
of the superconducting transition temperature shows that for small iron
concentration x the Pd_1-xFe_x layer is likely to be in the paramagnetic state
for very thin films whereas ferromagnetic order is established for x>=0.13. The
parallel critical field B_c2II(T) exhibits a crossover from two-dimensional
(2D) behavior where the Nb films are coupled across the interlayer, towards a
2D behavior of coupled Nb films with increasing d_PdFe or x. This 2D-2D
crossover allows a determination of the penetration depth xi_F of Cooper pairs
into the Pd_1-xFe_x layer as a function of x. For samples with a ferromagnetic
interlayer xi_ is found to be independent of x.Comment: 9 pages, 8 figure
Model calculations of the proximity effect in finite multilayers
The proximity-effect theory developed by Takahashi and Tachiki for infinite
multilayers is applied to multilayer systems with a finite number of layers in
the growth direction. The purpose is to investigate why previous applications
to infinite multilayers fail to describe the measured data satisfactorily.
Surface superconductivity may appear, depending on the thickness of the
covering normal metallic N layers on both the top and the bottom. The
parameters used are characteristic for V/Ag and Nb/Pd systems. The nucleation
process is studied as a function of the system parameters.Comment: 12 pages, 15 figures, RevTe
Confinement and Quantization Effects in Mesoscopic Superconducting Structures
We have studied quantization and confinement effects in nanostructured
superconductors. Three different types of nanostructured samples were
investigated: individual structures (line, loop, dot), 1-dimensional (1D)
clusters of loops and 2D clusters of antidots, and finally large lattices of
antidots. Hereby, a crossover from individual elementary "plaquettes", via
clusters, to huge arrays of these elements, is realized. The main idea of our
study was to vary the boundary conditions for confinement of the
superconducting condensate by taking samples of different topology and, through
that, modifying the lowest Landau level E_LLL(H). Since the critical
temperature versus applied magnetic field T_c(H) is, in fact, E_LLL(H) measured
in temperature units, it is varied as well when the sample topology is changed
through nanostructuring. We demonstrate that in all studied nanostructured
superconductors the shape of the T_c(H) phase boundary is determined by the
confinement topology in a unique way.Comment: 28 pages, 19 EPS figures, uses LaTeX's aipproc.sty, contribution to
Euroschool on "Superconductivity in Networks and Mesoscopic Systems", held in
Siena, Italy (8-20 september 1997
The Study of the Proximity Effect in Mg/Nb Multilayers
The proximity effect in multilayers of alternating superconducting and normal materials has been studied extensively over the years on various systems due to its transport properties of the entire system. In this work, Mg/Nb multilayer thin films were investigated through experimental methods and compared to the theoretical calculations. The crystal structured was studied to observe if the films followed the bi-phase diagram.
Firstly, a study of the crystal structure of the films was attempted through X-ray diffraction (XRD) measurements. The XRD images obtained were compared with DFT calculations for Mg/Nb multilayers to check if the films fell into the expected regions of the bi-phase diagram. The XRD results were not conclusive.
Next, the resistivity of all the films was measured to study the superconducting transition temperature of each of the films. The results were compared with calculations using the Cooper-de Gennes proximity effect model. The measured transition temperatures were a good match for the calculations, which points to Cooper-de Gennes being an appropriate model for this system, as long as the films are in the Cooper limit.
The upper critical field of the films was examined both parallel and perpendicular to the film. The angular dependence of the upper critical field was also studied. Comparing the results with the theoretical calculations for 3D and 2D upper critical field, it was found that the films matched the 2D expression for the upper critical field
Magnetoresistance of Junctions made of Underdoped YBCO Separated by a Ga-doped YBCO Barrier
We report magnetoresistance measurements of ramp type
superconductor-normal-superconductor (SNS) junctions. The junctions consist of
underdoped (YBCO) electrodes separated by a barrier of
. We observe a large positive magnetoresistance,
linear in the field. We suggest that this unusual magnetoresistance originates
in the field dependence of the proximity effect. Our results indicate that in
underdoped YBCO/N/YBCO SNS structures, the proximity effect does not exhibit
the anomalously long range found in optimally doped YBCO structures. From our
data we obtain the diffusion coefficient and relaxation time of quasiparticles
in underdoped YBCO.Comment: 5 figures, accepted for publication in Physical Review
Quantum size effects on the perpendicular upper critical field in ultra-thin lead films
We report the thickness-dependent (in terms of atomic layers) oscillation
behavior of the perpendicular upper critical field in the
ultra-thin lead films at the reduced temperature (). Distinct
oscillations of the normal-state resistivity as a function of film thickness
have also been observed. Compared with the oscillation, the
shows a considerable large oscillation amplitude and a phase shift. The
oscillatory mean free path caused by quantum size effect plays a role in
oscillation.Comment: 4 pages, 4 figure
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