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  • 1
    Electronic Resource
    Electronic Resource
    Electron-spin resonance in single crystals of YBa2Cu3O7−x and Bi4/3Pb2/3Sr2CaCu2O8+x (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5064-5066 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on electron-spin resonance on single crystals of YBa2Cu3O7−x and Bi4/3Pb2/3Sr2CaCu2O8+x at 9 GHz. While in the YBCO there was no observable ESR signal in the normal state (above Tc) or in the superconducting state (below Tc), we did observe a large microwave nonresonant absorption below Tc at low field values (H〈200 Oe). We attribute this form of absorption to fluxoid formation below Tc. In the BiPbSrCaCuO single crystals, a significantly different result was found in that an electron-spin-resonance signal was measured both above and below Tc, besides the low-field absorption occurring only below Tc. The g value was found to be 2.055 and reasonably constant with temperature from 300 to 4 K with H parallel to the c axis. We attributed the ESR line to Cu++ ion excitation. The ESR signal increased as T decreased from 300 K to Tc and the variation with temperature fits a Boltzmann statistics law. Below Tc the ESR signal remained constant as T was decreased below Tc. We explained this result in terms of two competing statistical effects. One effect is due to the fact that the ESR signal in the fluxoid region increases as the Boltzmann factor, but the fluxoid density decreases by the same factor. The net effect is that the ESR signal is constant with temperature below Tc. Hence, this is a clear demonstration of statistics involved in the formation of fluxoids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344671
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  • 2
    Electronic Resource
    Electronic Resource
    Microwave absorption in the presence of dc transport current in polycrystalline YBCO (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5076-5078 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-field microwave absorption in polycrystalline YBa2Cu3O7−x was measured as a function of dc current applied through the sample at various temperatures below Tc. The peak-to-peak value of the magnetically modulated microwave absorption (MMMA) signal increases with dc current at a fixed temperature. Above a threshold value of the current, the absorption signal level rapidly drops to zero, indicating quenching of superconductivity. If this critical current is plotted as a function of temperature, the results can be explained on the basis of the flux creep model. The MMMA signal obeys a scaling rule as predicted by the flux creep model. We conclude that flux creep limits the critical current density in these materials; also, this presents a new way of measuring critical current densities while using only a two-contact method. It gives some insight into the relationship between microwave properties and dc transport phenomena in these superconductors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344675
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  • 3
    Electronic Resource
    Electronic Resource
    Microwave induced nonlinearity in low frequency biased YBCO superconducting weak link rings (abstract) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6652-6652 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We fabricated weak link rings using YBCO thin films deposited on the single crystal MgO substrate by laser ablation. The dimensions of the microbridges in the rings were between 0.5–1 μ in length and 500 A(ring)–0.5 μ in width which were made by focused ion beam milling. We biased the ring by Faraday induction voltage while monitoring the voltage across the microbridge. The frequency of the input signal was varied between 10 kHz and 5 MHz. When we superimposed a microwave signal (2–18 GHz) to the ring, below the superconducting transition temperature (Tc), we observed strong nonlinearities in the voltage measured across the microbridge. The microwave frequency was chosen to be close to the ring natural electromagnetic resonance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352544
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetically modulated microwave absorption measurement of the penetration depth in a polycrystalline YBa2Cu3O7−x thin film : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4891-4893 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In previous work, a magnetically modulated microwave absorption (MMMA) technique to measure the Ginzburg–Landau parameter κ=(Λ/ξ) in high-Tc superconductors (bulk samples of YBCO) was described. In this work, how this technique can be applied to the measurement of the London penetration depth Λ is described. Data are reported for the temperature variation of Λ in a well-characterized c-axis-oriented polycrystalline thin film of YBa2Cu3O7−x, prepared by a pulsed laser deposition technique. For low temperatures, Λ(0)(approximately-equal-to)3640 A(ring) with the microwave electric field oriented parallel to the c axis. The temperature dependence of Λ(0)/Λ(T) can be well described by the two-fluid model. The data are also reasonably fit by a BCS model, however the MMMA technique (in the work here reported) does not have the resolution at low temperatures to obtain strong quantitative evidence for an energy gap Δ (even if it exists).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348215
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  • 5
    Electronic Resource
    Electronic Resource
    Measurement of kappa in high Tc superconductors (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4143-4145 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The experimental magnetic-field derivative of the microwave absorption signal, obtained using electron paramagnetic resonance techniques, has a line shape that depends on the Ginzburg–Landau model parameter κ of the superconducting sample at a given temperature. The type-II superconducting equation of state can be utilized to describe the drop in the output microwave power derivative, from its maximum at H (approximately-equal-to) Hc1 to its much lower values when H (very-much-greater-than) Hc1, in order to estimate the values of κ. The technique also allows for the experimental determination of hysteretic behavior in B as a function of H.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348432
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  • 6
    Electronic Resource
    Electronic Resource
    Measurements of anisotropic characteristic lengths in YBCO films at microwave frequencies : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5865-5867 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We used microwave self-resonant and magnetically modulated microwave absorption techniques to measure the London penetration depth, λ, and coherence length, ξ, in the direction parallel and perpendicular to the a–b plane of YBCO films. We found that both λ and ξ were anisotropic; it appeared that the value of λ(parallel)(0) was about 1800 A(ring) and λ⊥(86.5) about 26 000 A(ring), where λ(parallel) is the penetration depth for the applied microwave electric field parallel and λ⊥ perpendicular to the film plane (c-axis is perpendicular to the film plane). We deduced ξ(parallel) to be equal to 129 A(ring) and ξ⊥ 40 A(ring) at 86.5 K. The anisotropy factor γ we determined to be about 3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353554
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  • 7
    Electronic Resource
    Electronic Resource
    Excess current in shunted Josephson weak links (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 8195-8197 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a variety of Josephson weak links the resistively shunted junction model does not properly describe observed excess currents in the voltage current characteristics. A modification of the model is proposed which more adequately describes experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356519
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  • 8
    Electronic Resource
    Electronic Resource
    Heterodyne microwave mixing in a superconducting YBa2Cu3O7−x coplanar waveguide circuit containing a single engineered grain boundary junction : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6962-6964 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The purpose of this work was to utilize the nonlinear current-voltage properties of induced grain boundaries in high temperature superconducting YBa2Cu3O7−x thin films to fabricate a planar microwave mixer. The experiment involved constructing a coplanar waveguide microwave circuit, the center conductor of which had a constriction patterned in it containing a single high angle grain boundary, thus forming a weak link junction. Analysis was provided by use of the resistively shunted junction model with excess current.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358088
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  • 9
    Electronic Resource
    Electronic Resource
    Flicker noise in YBa2Cu3O7−δ bicrystal grain boundary junctions in weak magnetic fields (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1307-1309 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Flicker noise in c-axis oriented long YBCO bicrystal grain boundary junctions was characterized as a function of temperature, biasing conditions, and magnetic field applied perpendicular to the a–b plane over a wide range of temperatures from 15 K to over 70 K. Aperiodic variations, as a function of magnetic field, were observed in both the junction voltages, VJ, and the flicker noise magnitude under constant current bias as the magnetic field was scanned from 0 to 8 G. The noise magnitudes were found to peak at the minima of VJ. Analyses of the field dependencies of the magnitudes and the functional form of the voltage noise power spectra show that the noise did not arise from thermally activated flux motion. Based on the dependencies of the noise power spectra on the bias current and the dynamic resistance of the junction, we conclude that the noise originates from the fluctuations of the critical current of the devices most likely due to trapping of carriers or defect motion within the grain boundary. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114522
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  • 10
    Electronic Resource
    Electronic Resource
    ac Hall measurements on high-Tc superconductors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4545-4546 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hall experiments are carried out normally in bulk materials where a dc current is applied perpendicular to a static magnetic field. Since the dc Hall coefficient is small for type-II superconductors at temperatures well below the transition temperature Tc, the possibility of measuring the Hall coefficient of the superconductor under ac conditions is explored. It is found that the ac Hall coefficient can be readily detected through the measurement of the reflected microwave beam, whose polarization has been rotated 90° away from the incident wave irradiating on the surface of a high-Tc superconducting material biased by a dc magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344863
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