摘要:

Josephson junctions are essential components in high‐temperature superconductive integrated circuits. YBaCuO/Nb‐doped SrTiO3/YBaCuO epitaxial Josephson junctions have been designed, fabricated, and tested. The YBaCuO and Nb‐doped SrTiO3films were deposited by off‐axis sputtering. Both dc and ac Josephson effects have been observed and the supercurrent persists up to 80 K. The critical current density is an exponential function of the barrier layer thickness. The product of critical current and normal resistance is between one and three millivolts. A superconducting quantum interference device made of the junctions displays magnetic field modulation of critical current.

ISSN:0003-6951    

DOI:10.1063/1.104537

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The roles of composition and oxygen pressure ininsitugrowth of superconducting YBaCuO films have been studied. Anomalous results are observed at low oxygen pressure. Off‐stoichiometric, Ba‐deficient films have superior superconducting properties and more bulk‐like crystal structure compared to films made on the 1:2:3 stoichiometry. Films made at low pressure have an expandedcaxis compared to the bulk value, although theirTc’s are only slightly depressed.Tcandc‐axis lattice parameters are reported as a function of the deposition conditions.

ISSN:0003-6951    

DOI:10.1063/1.104538

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Electromigration failure in highly oriented YBa2Cu3O7−xthin films below the superconducting transition temperature is reported here for the first time. The film on SrTiO3failed at 86 K, 2.3×105A cm−2; while that on LaAlO3failed at 84 K, 9.3×105A cm−2. Scanning electron microscopy and energy dispersive x‐ray analysis of the films after failure shows that Cu migrates preferentially away from the failure region towards the electrode.

ISSN:0003-6951    

DOI:10.1063/1.104539

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report the successful preparation of 1212 PbSrYCaCuO thin films by laser ablation. The films are growninsituon (100)LaAlO3at the relatively low substrate temperature of 610 °C. The starting composition of the target is not that of the superconductor produced. Its composition was choosen to yield the 2213 PbSrYCaCuO phase, but the structural analysis shows a predominantly 1212 film with a small impurity phase. The films are highly oriented and show superconducting transitions with onsets at 90 K and zero resistance by 75 K.

ISSN:0003-6951    

DOI:10.1063/1.104540

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report high‐resolution transmission electron microscopy and electron diffraction studies of the heteroepitaxial superconductor‐insulator‐superconductor system YBa2Cu3O7−x‐SrTiO3‐YBa2Cu3O7−xdeposited on polished (001)MgO substrates byinsitulaser ablation. The resulting films grow epitaxially and consistently preserve a parallel orientation between the close‐packed (001)YBa2Cu3O7−xplanes and (001)SrTiO3planes over the entire trilayer, even in the presence of ledges or steps along vicinal interfaces. Although the interface regions showed strain occasionally relieved by stacking faults, they were free of disorder and any evidence of impurity phases. The observed epitaxial growth is very likely responsible for the excellent electrical properties found in similarly constructed multilayer interconnects.

ISSN:0003-6951    

DOI:10.1063/1.104541

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We show that flux pinning in Bi2(Sr,Ca)3−xCu2O8+&dgr;is increased by intentional deviations in cation nonstoichiometry. Polycrystalline samples of alkaline earth‐deficient composition (x=0.24–0.32) show a larger irreversibility in magnetization (&Dgr;M), and a slower decay of &Dgr;Mwith both increasing field and time than stoichiometric compositions. The difference between compositions grows with increasing field out to 5 T, and is greatest atT≤20 K but still significant at 40 K. The critical state model yields a difference in intragranular current density (Jcm) at 20 K and 2 T of ≳102between stoichiometric andx=0.3 compositions. Flux pinning energies determined from relaxation of magnetization are several times greater for cation‐deficient than for stoichiometric compositions. These improvements are only achieved upon slow cooling or low‐temperature annealing, indicating that defect clustering or incipient precipitation is necessary to form more effective pinning defects.

ISSN:0003-6951    

DOI:10.1063/1.104542

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thin films of (Ca,Sr)CuO2, the parent material of highTccuprate superconductors, have been formed by the laser ablation method under molecular beam epitaxial condition, and the growth mechanism has been investigated with reflection high‐energy electron diffraction (RHEED). Analyses of RHEED patterns and intensity oscillations show that this material grows with two‐dimensional layer growth. When all the metal elements are supplied simultaneously in NO2atmosphere, the layer growth occurs with the unit‐cell layer of (Ca,Sr)CuO2. Furthermore, it has become evident that the growth unit can be separated into Ca (Sr) atomic layer and CuOxatomic layer by monitoring the RHEED intensity oscillation. The successive supply of each metal element leads to one atomic layer growth of this material.

ISSN:0003-6951    

DOI:10.1063/1.104543

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Delay‐time measurements with a microwave setup, where a step narrowing in the waveguide simulates a quantum mechanical potential barrier, have been performed even beyond the cutoff. This allows experimental measurements in a very accessible temporal range of the order of nanoseconds. The results, interpreted as tunneling times, are compared with the existing quantum mechanical models, translated into the electromagnetic framework.

ISSN:0003-6951    

DOI:10.1063/1.104544

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Local cation order approaching ideal bulk termination was found for cleaned (001) surfaces of YBa2Cu3O7crystals by ion‐channeling surface‐peak analysis. Surfaces etched in dilute CH3OH:Br2and ultrasonically agitated in CH3OH to dislodge the Br2appear terminated preferentially by the Cu‐O ‘‘double‐plane’’ sequence, containing less than 1/2‐cation monolayer of surface disorder. Planar polishing with ion beams incident at a glancing angle on a rotating crystal leaves residual disorder as low as ∼8 A˚, damage which is readily removed by a light chemical etch.

ISSN:0003-6951    

DOI:10.1063/1.104515

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.105248

出版商:AIP    

年代:1991

数据来源: AIP