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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 3822-3824 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A versatile, compact, constant current-voltage, bipolar power source for quasi-static or derivative measurements of the characteristics of superconducting junctions has been developed. The circuitry is based on a negative feedback strategy that is effective in maintaining constant current-voltage behavior at the junction itself and all lead resistances are included in the feedback loop. Constant currents and voltages can be delivered of up to ±0.5 A and ±0.75 V, respectively. Both fast and slow sweeps, as well as a single sweep mode, are available in variable ranges. The single sweep feature is used to avoid heating effects in low resistance junctions which are not in good thermal contact with a thermal reservoir (e.g., liquid 4 He).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2643-2645 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transverse magnetoresistance and Hall effect have been studied for n-type gray tin epilayers grown on (001)CdTe substrates by the molecular beam epitaxy technique. Shubnikov–de Haas oscillations were observed in samples having Hall mobilities ≥104 cm2 /V s at low temperatures. Measurements were carried out using both the dc method and field modulation techniques in the temperature range from 1.2 to 10 K and in magnetic fields up to 10 T. Beat patterns were observed in the Shubnikov–de Haas spectra which we ascribe either to inhomogeneous doping, arising from the diffusion of Cd and Te from the substrate, or to quantization of the motion in the direction parallel to the film normal. The Shubnikov–de Haas carrier concentration of a 1210 A(ring) film was determined to be nSdH =2.3×1017 cm−3, in good agreement with the Hall density.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4240-4246 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the magnetic hysteresis loops and temperature dependent trapped fields in melt-textured YBa2Cu3O7−δ samples before and after p+ and 3He++ irradiation using a Hall effect magnetometer (HEM) as well as a commercial vibrating sample magnetometer (VSM). For proper 3He++ fluence, the critical current density may be enhanced by a factor of 10. Calculations based on various critical state models show that before the irradiation, the hysteresis loops can be well accounted for by a critical current density of a modified power law field dependence Jc(T,B)=J0(T)/(1+B/B0)n with n=1/2; after the irradiation, the best fit has been achieved by using an exponential form such as Jc(T,B)=J0(T)exp(−B/B0), where B0 is a model dependent parameter. Jc and its field dependence deduced from HEM hysteresis loops are in good agreement with those deduced from the VSM loops, suggesting that the Hall effect magnetometer can be conveniently used to characterize bulk high Tc oxide superconductors.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1573-1575 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of YBaCu(F)O were deposited on SrTiO3(100) substrates by multilayer deposition from three electron guns containing Y, BaF2, and Cu under a pressure of 5×10−5 Torr of O2. The films were later annealed in a separate chamber under a flowing O2-H2O atmosphere. X-ray diffraction studies reveal that the resulting structure is highly oriented with the a axis perpendicular to the substrate. Scanning electron micrographs show a morphology consisting of an array of orthogonal, interconnecting bars with well-developed junctions. High-resolution electron microscopy and electron diffraction patterns show that these junctions are atomically abrupt and that the associated c axes are mutually perpendicular. These epitaxial films show a sharp resistive transition with Tc(R=0) as high as 90 K. The zero field critical current density, determined from magnetization measurements, is 2.9×106 A/cm2 at 4.2 K and 5.0×104 A/cm2 at 77 K.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2949-2954 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the static I–V characteristics and cavity modes in stacked double Nb/AlOx/Nb Josephson junctions. In junction stacks consisting of two junctions with identical critical currents Ic, the Ic vs H characteristics have been observed to deviate from the usual Fraunhofer pattern in the small junction limit; the data are consistent with a model involving a structural phase transformation to a triangular vortex lattice with increasing H. In a finite voltage state interlayer coupling leads to splitting of the Swihart mode, which manifests itself as Fiske steps with different voltage spacings. The results provide clear evidence that the two junctions in the stack do phase lock. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of YBaCuO have been prepared with (1) the a axis perpendicular to (100) SrTiO3 ; (2) the c axis perpendicular to (100) SrTiO3 ; and (3) the [110] axis perpendicular to (110) SrTiO3. Films were fabricated using a multilayer deposition technique involving three electron guns containing Y, BaF2, and Cu under a pressure of 5×10−5 Torr of O2. As deposited films, which contained polycrystalline and amorphous regions, were later annealed in a furnace under a flowing O2-H2 O atmosphere. X-ray diffraction patterns as well as scanning electron microscopy and high-resolution electron microscopy images confirm that the films are highly oriented, essentially epitaxial. The a-axis oriented film exhibits zero resistance at 90 K and a critical current density of 2.9×106 A/cm2 at 4.2 K while the c-axis oriented film exhibits a Tc of 88 K and a Jc of 0.9×107 A/cm2 at 4.2K; the Jc values were determined magnetically. The [110]-orientation film shows the sharpest transition with a transition width of 1 K and zero resistance at 85 K.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5360-5366 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous Si/Nb superlattices with modulation wavelengths ranging from 20–200 A(ring) have been grown on sapphire substrates at 100–150 °C by dual e-beam evaporation in an ultra-high-vacuum (UHV) system. The low-angle x-ray diffraction data can be accounted for by a symmetric trapezoidal composition profile model. The intermixing at the layer interfaces is estimated to be 6–12 A(ring), depending on the substrate temperatures. In the film growth direction, the coherent domain size of the polycrystalline Nb layers scales with the Nb layer thickness. High-resolution transmission electron microscopy reveals the existence of microcrystallites in the 20-A(ring)-thick amorphous Nb layers; also resolved are the microstructure of the substrate/superlattice and superlattice/thick-Nb layer interfaces. In addition, Auger depth profiling results are also consistent with the expected composition modulation.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2127-2131 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A sputtering deposition system has been developed to grow high-quality superconductor/insulator multilayers specifically for use in fabricating vertically stacked Josephson junctions. A unique feature of the design is the computer control of all parameters involved in the repetitive deposition of multilayers. The computer is interfaced with stepper motors that position the substrate, and shutter wheels. Additional computer controlled stepper motors allow in situ changing of up to five contact masks. The computer is also interfaced to a gas flowmeter that controls the partial pressure of the inert and reactive sputtering gases. High-quality, reproducible multilayer films have been produced and are described. Stacked Josephson junctions have been patterned with the multilayer films and some of their electrical characteristics are presented. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1376-1378 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetization and critical magnetization current densities of sinter-forged YBa2Cu3O7−δ samples of nearly theoretical density have been studied. The magnetization curves can be well fitted by Kim's critical state equation Jc(B)=α/(B0+B) with a flat plate geometry. The results revealed an anisotropy in the lower critical field and the critical current density with respect to the forging axis. The deduced critical current density in the favorable direction is larger than the value of isotropic polycrystalline samples.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1194-1196 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Y-Ba-Cu-O thin films have been deposited on MgO substrates by dc magnetron sputtering from a stoichiometric YBa2Cu3O7−δ target, after which they are subjected to a short heat treatment. Zero resistance is routinely achieved near 60 K, and one film shows zero resistance at 68.0 K.
    Type of Medium: Electronic Resource
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