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  • 1
    Electronic Resource
    Electronic Resource
    The microwave surface impedance of granular high TC superconductors in dc magnetic fields: Its relationship to frequency dependence (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4103-4108 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface impedance of bulk and thick film granular high temperature superconductors has been studied. The static magnetic field, temperature, and frequency dependence of the surface impedance have been analyzed in terms of the weakly coupled grain model. Accurate quantitative predictions of the frequency dependence of the surface resistance are made using this model. The model also quantitatively accounts for the negative magnetic field coefficient of the effective rf penetration depth. The rf penetration depth is a maximum when the ratio of penetration depth to skin depth is 0.930.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355989
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  • 2
    Electronic Resource
    Electronic Resource
    A contactless method for measurement of the critical current density and critical temperature of superconducting films (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 996-1004 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new method is described for measuring the critical current density and transition temperature of a superconducting film without making contact to it or modifying it in any way. This technique is particularly well suited for use with high transition temperature oxide films which are notoriously irreproducible and sensitive to patterning. It consists of positioning a flat, multiturn coil near the film surface and driving the coil with an audio frequency sine-wave current. Induced shielding currents flow in the film. We have calculated the radial dependence of the induced currents and show that the induced current density is zero at the coil center, rises to a maximum near the mean radius of the drive coil, and then falls off rapidly as the radius continues to increase. A measurement of the critical current per length can be obtained by monitoring the development of odd harmonic voltage components across the coil as the drive current is increased. We find that this measure of nonlinearity in the coil–film system increases abruptly when the maximum induced current equals the critical current. The critical current obtained by this inductive measurement has been demonstrated to give nearly the same value as that obtained by a transport measurement. Other advantages to this inductive measurement approach include: sensitivity only to intergranular critical current, and an ability to accommodate large substrates. Finally, with only minor modification to the electronics used to measure Jc, the superconducting transition temperature of the sample may be measured as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141991
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  • 3
    Electronic Resource
    Electronic Resource
    A system for in-situ pressure and ac susceptibility measurements using the diamond anvil cell: Tc(P) for HgBa2CuO4+δ (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 992-997 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Substantial improvements have been made in the sensitivity of an ac susceptibility measurement system which determines the pressure dependence of the superconducting transition temperature, Tc(P). The pressure, P, is determined near Tc from the position of the R1 and R2 fluorescence peaks from ruby chips. The system was used to determine Tc(P) for several high Tc single crystals, but was not sufficiently sensitive to determine Tc(P) of polycrystalline samples for HgBa2CuO4+δ. This motivated us to improve the sensitivity of our system. Other parts of the system and the data analysis procedures also have been improved. As a demonstration, Tc(P) of HgBa2CuO4+δ polycrystal to 4 GPa is presented. The improvement of the system using the diamond anvil cell opens the possibility of measuring Tc above 10 GPa and on smaller samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144878
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  • 4
    Electronic Resource
    Electronic Resource
    Critical current enhancement in proton-irradiated Tl2CaBa2Cu2O8 films (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1119-1121 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured changes in the superconducting transition temperature Tc and critical current density Jc of epitaxial Tl2CaBa2Cu2O8 films upon exposure to 2 MeV protons. Jc was measured inductively at 4.2 and 77 K and in fields of H=0 and 0.2 T. At 77 K and H=0, Jc decreases monotonically with increasing fluence Φ. The rate of decrease is about 1.8 times greater than for YBa2Cu3O7 films, even though the rate of change of Tc with Φ is comparable. At 4.2 K, Jc is initially enhanced, even at H=0. The maximum observed increase is 34% (to 8 MA/cm2) at Φ≈1016 protons/cm2 and H=0.2 T. This enhancement is attributed to pinning of magnetic flux lines by proton-induced defects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347384
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  • 5
    Electronic Resource
    Electronic Resource
    Simultaneous imaging of dielectric properties and topography in a PbTiO3 crystal by near-field scanning microwave microscopy (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3295-3297 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use a near-field scanning microwave microscope to simultaneously image the dielectric constant, loss tangent, and topography in a PbTiO3 crystal. By this method, we study the effects of the local dielectric constant and loss tangent in the geometry of periodic domains on the measured resonant frequency, and quality factor. We also carry out theoretical calculations and the results agree well with the experimental data and reveal the anisotropic nature of the dielectric constant. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126611
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  • 6
    Electronic Resource
    Electronic Resource
    Uniaxial dielectric anisotropy in Ba0.5Sr0.5TiO3 films studied by evanescent-probe microscopy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3872-3874 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric permittivity, tunability (Δε/ε), and loss tangent of Ba1−xSrxTiO3 (BST) films grown by pulsed-laser deposition are studied by near-field microwave microscopy. Based on theoretical simulations, a method is developed to measure the uniaxial dielectric anisotropy, ε⊥/ε(parallel), in BST films grown at different oxygen pressures. The measured ε⊥/ε(parallel) decreases with the film-growth oxygen pressure, consistent with the structural anisotropy. The films prepared at 50 mT, with ε⊥(approximate)ε(parallel), have the highest permittivity, tunability, and figure of merit. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1377628
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  • 7
    Electronic Resource
    Electronic Resource
    Critical-current enhancement in particle-irradiated cuprate semiconductors (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2600-2602 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed measurements have been made of the magnetic field (0〈H〈6 T) and temperature (10 K〈T〈100 K) dependencies of the critical current density jc in Tl2CaBa2Cu2O8 films before and after irradiation with incremental fluences (0〈Φ〈3×1016 cm−2) of 2 MeV protons. The results are interpreted quantitatively in terms of radiation-induced changes in (1) the critical temperature, (2) the rate of thermal flux creep, and (3) local scale superconductivity. Radiation-induced enhancements in jc are described by an expression which allows the fluence that maximizes jc to be predicted as a function of H, T, pinning energy, and particle type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105915
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  • 8
    Electronic Resource
    Electronic Resource
    Controllable alteration of the pinning energy in Tl2Ca2BaCu2O8 films by proton irradiation (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 252-254 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Irradiation with 2 MeV protons increases the vortex pinning energy in Tl2Ca2BaCu2O8 films. The maximum pinning energy occurs at a defect density that depends on (1) the density of flux pinning centers in the unirradiated film, (2) the ratio of pinning energies of the pre- and post-irradiation defects, and (3) the effectiveness of the incident particle in creating pinning centers. An explicit formula for the pinning energy as a function of fluence is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110357
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  • 9
    Electronic Resource
    Electronic Resource
    Detection of a metastable magnetic phase in the La1.85Ba0.15CuO4−y system (1987)
    Springer
    Journal of low temperature physics 68 (1987), S. 419-425 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have made samples of La1.85Ba0.15CuO4−y with varying heat treatments. We have measured their dc magnetization and electron paramagnetic resonance, and have examined them by electron microscopy and electron diffraction. For samples annealed only a few hours, cooling the material below 5 K causes a magnetic transition and a thermal hysteresis. These observations, taken with the EPR data, suggest a possible spin-glass or ferromagnetic phase. Annealing samples in an oxygen atmosphere appears to remove that magnetic phase. For the phase with the K2NiF4 structure, no superlattice spots are seen in electron diffraction at room temperature or at 77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00682306
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  • 10
    Electronic Resource
    Electronic Resource
    Proton-induced reduction ofR s, Jc, andT c in YBa2Cu3O7−δ thin films (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 57-60 
    Details
    ISSN: 1572-9605
    Keywords: Thin films ; radiation damage ; surface resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have explored the effect of 2-MeVH+ irradiation on the superconducting transport properties of thin films of YBa2Cu3O7−δ [T c, Jc(B=0; 77 K, 4.2 K), andR s(36 GHz;T)]. The inductively measured critical temperatureT c changed slowly and uniformly (∼2 K per 1016/cm2) for fluences less than ∼3×1016/cm2. Beginning at ∼3–4×1016/cm2, the superconducting transition broadened and dropped more quickly with fluence. The critical current density measured at 77 and 4.2 K changed roughly linearly with fluence. The microwaveT c (as defined by the sharp transition inR s as a function of temperature) resembled the low-frequency inductiveT c measurement at low fluences but was depressed more strongly for large fluences. The residual surface resistance (∼6–10 mΩ) was not affected for fluences up to 5×1016/cm2. We have interpreted the sudden and reproducible reduction in the microwaveT c transition as a sensitive indicator of disruption in the copper-oxygen chain sublattice and compared the proton-induced change to that observed in oxygen gettering studies of bulk materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618298
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