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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    New magnetic material spectroscopy (abstract) : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4243-4243 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sensitive commercial electron paramagnetic resonance (EPR) spectrometers are able to measure 10∧13 spins. Using a high Tc weak link, we were able to measure FMR on yttrium ion garnet (YIG) films which were exposed to an effective area of 3 nm by 15 micrometers. Given that this is the area of excitation and the thickness of the YIG was 0.5 micrometers, we could measure less than 10∧9 spins in a YIG film. Our weak link was fabricated by patterning a 0.5 micrometer thick film of YBCO down to a 15 micrometer wide bridge across an artificial grain boundary in an MgO substrate. Our technique uses the ac Josephson effect to generate a microwave field which couples into a YIG film which is placed in intimate contact atop the link. The frequency of this microwave field is proportional to the voltage across the weak link. The absorption of the microwaves by the YIG will affect the voltage versus current behavior across the weak link. For a YIG film of 0.5 micrometers thickness, we measured an in-plane linewidth of 125 Gauss using the weak link technique. The FMR linewidth measured by a conventional EPR technique was 40 Gauss. This implies that the excitation by the weak link may be nonuniform. We present data which illustrate this effect and numerical results for the corresponding circuit model. Our conclusions are that we have developed a viable spectroscopy to characterize extremely local magnetic interactions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365134
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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Effects of dc transport current on low-field microwave absorption in ceramic superconducting YBCO samples (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2182-2185 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of dc transport current on low-field microwave absorption have been investigated systematically on bulk ceramic YBa2Cu3O7−δ samples. At a fixed temperature T, the critical current Ic(T) at which the electron paramagnetic resonance (EPR) signal vanishes varies linearly with T. The EPR absorption characteristics obey a scaling rule in accordance with the flux creep model. A revised version of the flux creep model is also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345561
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