Critical currents of semiconductor-coupled Josephson weak links

1991 ◽  
Vol 27 (2) ◽  
pp. 2589-2593 ◽  
Author(s):  
A.W. Kleinsasser
Keyword(s):  
Critical Currents ◽  
Weak Links

Microstructure of thin YBa2Cu3O7−δ films

1990 ◽  
Vol 48 (4) ◽  
pp. 8-9
Author(s):  
M. Grant Norton ◽  
C. Barry Carter
Keyword(s):  
Thin Films ◽  
Film Growth ◽  
Weak Link ◽  
Critical Currents ◽  
Weak Links ◽  
High Tc ◽  
Fundamental Interest ◽  
Early Stages ◽  
Transmission Electron ◽  
Patterned Films

The microstructure of superconducting thin-films often strongly influences their electrical properties. The actual microstructure of the film will be dependent on the nucleation and early stages of film growth, although the substrate will also be expected to exert an influence during the early stages of growth by the establishment of epitaxy. The highest critical currents have been obtained with films grown on SrTiO3, however MgO is of fundamental interest because patterned films on MgO have been shown to possess Josephson weak-link structure. The presence of the Josephson weak-links has been correlated with the occurrence of misaligned grains in films grown on MgO. Ultra-thin films of high-Tc superconductors are of interest for understanding the properties of these materials and may also be of use in technical applications.The microstructure of ultra-thin YBa2Cu3O7−δ films prepared by pulsed-laser ablation onto (001)- oriented MgO has been studied using transmission electron microscopy (TEM) and selected-area diffraction (SAD).

PERCOLATION IN SUPERCONDUCTING CUPRATES: RESISTIVITY AND CRITICAL CURRENTS

1989 ◽  
Vol 03 (05) ◽  
pp. 719-732 ◽  
Author(s):  
J. HALBRITTER
Keyword(s):  
Superconducting State ◽  
Critical Currents ◽  
Weak Links ◽  
Geometrical Factor ◽  
Planar Defects ◽  
Intrinsic Values ◽  
Flux Motion ◽  
Current Path ◽  
Pair Tunneling ◽  
Current Flows

Weak links in metallic cuprates yield complicated percolative conduction networks enhancing the intrinsic resistivity ρi(T) = αiT + ρi0L to: [Formula: see text] with ρb describing the weak links and a geometrical factor p ≥ 1. In most cases "single crystals" and "epitaxial" films show insulating intragrain weak links yielding p ≈ 3 and Σρb ≪ ρi(100 K ), like good sintered YBa 2 Cu 3 O x. Rarely are the intrinsic values αi ≈ 0.5 μΩ cm/K and ρi(100 K ) ≈ 50 μΩ cm observed. In the superconducting state the intrinsic resistivity pi(T) vanishes and then the critical transport current density jc (B, T) is given by the superconducting aspects of conducting weak links: [Formula: see text] Here, jCJ (jCG) stands for Josephson junctions at intergrain (intragrain) weak links and jCP for pinning. ps(B, T) stands for current path systems changing with B-field and temperature. jCJ and jCG depend crucially on the care in preparation and alignment of the [Formula: see text]-planes, where the current flows, but values jCJ (0.77 K ) ≈ 103 A/cm 2 and jCG (0.77 K ) ≈ 105 A/cm 2 seem typical. Weak links are related to planar defects where large and small angle grain boundaries are dominant. jCP is shadowed by jCJ and jCG but jCP ≈ 106 A/cm 2 are inferred from experiment. The time-, temperature-, B-field- and voltage-dependencies of the current in — and in the transition to — the superconducting state are analyzed. Evidence is presented for arrays of microbridges being "electrically" the planar defects. These microbridges are typical superconductor-normal-conductor-superconductor (S-N-S) junctions, where pair tunneling is reduced by factors 10–103 as compared to single particle, normal tunneling. The reduced pair tunneling is due to normal conductors coating cuprates being related to O-disorder and the tetragonal phase, which also occur by radiation damage. The time and voltage dependence implies rapid flux motion or flux creep along the planar defects causing noise and rf residual losses.

Nondestructive Analysis of Bi2212 Bulk Superconducting Ceramics in the C-Axis Direction

2016 ◽  
Vol 869 ◽  
pp. 29-34
Author(s):  
Antonio Renato Bigansolli ◽  
T.G. da Cruz ◽  
Durval Rodrigues Jr.
Keyword(s):  
Magnetic Field ◽  
Grain Size ◽  
Applied Magnetic Field ◽  
Structural Parameters ◽  
Processing Technique ◽  
Critical Currents ◽  
Weak Links ◽  
Critical Temperatures ◽  
Axis Direction ◽  
Average Grain Size

The use of superconductors of high critical temperatures in applied superconductivity leads to higher operation temperatures and economy of cryogenic fluids. High temperature superconductor materials exhibits limited transport properties due to grain boundary weak-links and anisotropy on the critical currents. The texturing development in these superconductors decreases in an efficient way the number of high-angle grain boundaries, increasing the values of the critical current densities. Several quantitative analysis methods have been developed to study the morphologic and topologic characteristics improving our understanding of structural parameters. In this work the grain size distribution characterization of Bi2Sr2CaCu2O8+δ Bi2212 superconductor bulk samples heat treated under the influence of an external applied magnetic field of 5T was carried out using a processing technique and analysis of images. The analyzed images were obtained by SEM in the c axis direction. All samples showed similar microstructures on both cases, but with the use of an external applied magnetic field during the heat treatments the average grain size decreased.

Scanning Electron Microscope Study of Superconducting Transport in a YBa2Cu3O7-δ thin film

1989 ◽  
Vol 47 ◽  
pp. 176-177
Author(s):  
R. C. Farrow ◽  
Don Monroe ◽  
W. S. Brocklesby ◽  
M. Hong
Keyword(s):  
Thin Film ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Local Heat ◽  
Beam Current ◽  
Critical Currents ◽  
Weak Links ◽  
Scanning Electron Microscope Study ◽  
Temperature Bias ◽  
Scanning Electron

By combining electron probing with current biasing at low temperatures a map of the transport characteristics of a mixed phase thin film superconductor can be obtained. The electron beam of a scanning electron microscope (SEM) acts as a local heat source. Under the proper conditions of temperature, bias current, and beam current, variations in the superconducting state can be mapped and compared to microstructure and chemical phase information. This method has recently been applied to high Tc superconductors to map critical currents and to identify weak links in superconducting paths. We discuss here the possible application of the technique to identify the superconducting phase within a matrix of non-superconducting material.The sample was an ∼1 μm thin film that was grown by sputtering from a YBa2Cu3O7-δ target onto a [001] SrTiO3 substrate. A more detailed description of the growth procedure is given elsewhere. The morphology, crystallinity, and stoichiometry of the samples were characterized in the SEM. The film had several chemical phases and a morphology consisting of large rectangular platelets (typical size 200х50 μm), covering ∼20-30% of the surface.

Characterization of Bi2212 Superconductor Bulk Samples by Digital Image Processing

2014 ◽  
Vol 975 ◽  
pp. 128-133
Author(s):  
Antonio Renato Bigansolli ◽  
Tessie Gouvêa da Cruz ◽  
Francisco Romário de Souza Machado ◽  
Durval Rodrigues Jr.
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Analytical Techniques ◽  
Critical Currents ◽  
Weak Links ◽  
Critical Temperatures ◽  
Heat Treated ◽  
Grain Distribution ◽  
Superconductor Bulk

The use of superconductors of high critical temperatures in applied superconductivity leads to higher operation temperatures and economy of cryogenic fluids. High temperature superconductor materials exhibits limited transport properties due to grain boundary weak-links and anisotropy on the critical currents. The texturing development in these superconductors decreases in an efficient way the number of high-angle grain boundaries, increasing the values of critical current densities (Jc). In this research the size grain distribution characterization of Bi2212 superconductor bulk samples heat treated under the influence of an applied external magnetic field of 5T was carried out combining processing and images analysis obtained by SEM and statistical methodologies. The objective is to investigate influence of an external magnetic field applied during the heat treatment profiles on the texturing of Bi2Sr2CaCu2O8+δ (Bi2212) bulk by using complementary analytical techniques.

Direct measurement of critical currents of individual weak links in DC interferometerby scanning laser microscope

Cryogenics ◽  
1994 ◽  
Vol 34 ◽  
pp. 879-881 ◽  
Author(s):  
A.V. Lukashenko ◽  
A.G. Sivakov ◽  
O.G. Turutanov ◽  
I.M. Dmitrenko ◽  
I.N. Chukanova
Keyword(s):  
Direct Measurement ◽  
Critical Currents ◽  
Scanning Laser ◽  
Weak Links

Magnetic-history-dependent critical currents in granular high-temperature superconductors: Dependence on defect structures and morphology

1989 ◽  
Vol 47 ◽  
pp. 186-187
Author(s):  
Martin P. Maley ◽  
Michael E. McHenry ◽  
Jeffrey O. Willis
Keyword(s):  
High Temperature ◽  
Critical Current ◽  
High Temperature Superconductors ◽  
Critical Currents ◽  
Weak Links ◽  
Small Scale ◽  
Defect Structures ◽  
Flux Lattice ◽  
Superconducting Coherence Length ◽  
Current Densities

Critical current densities, Jc’s, in conventional low temperature superconductors are controlled by defect structures that provide pinning for the magnetic flux lattice. High critical current densities and strong pinning have been observed in single crystals of the new oxide, high temperature superconductors (HTS) and have been ascribed to the presence of twin planes and to stoichiometry variations in the YBCO compound. Neutron irradiation studies have shown that intragranular Jc’s in YBCO can be strongly enhanced by the point defects introduced by irradiation. However, transport Jc’s determined by intergranular current transfer have remained dissappointingly low in bulk ceramic HTS materials. This has suggested a model of strongly superconducting grains separated by “weak links” that behave as Josephson tunnel junctions.The extraordinarily small superconducting coherence length ζo ∼ 10 A° in the HTS make them considerably more sensitive to small scale defects. Grain boundaries that act as pinning centers in conventional superconductors thus become barriers to current flow in the HTS.

High critical currents in Ag-BSCCO(2223) tapes: Are the grain boundaries really ‘weak-links’?

1993 ◽  
Vol 195 ◽  
pp. 503-506 ◽  
Author(s):  
SM Cassidy ◽  
LF Cohen ◽  
MN Cuthbert ◽  
JR Laverty ◽  
GK Perkins ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Critical Currents ◽  
Weak Links
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