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  • 1
    Electronic Resource
    Electronic Resource
    YBa2Cu3Ox Josephson junctions on a bicrystal sapphire substrate for devices in the millimeter and submillimeter wavelength ranges (1999)
    Springer
    Technical physics letters 25 (1999), S. 249-252 
    Details
    ISSN: 1090-6533
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract High-temperature superconducting Josephson junctions on bicrystal sapphire substrates were fabricated and investigated experimentally. The critical parameters of the junctions satisfy the constraints for the design of devices in the millimeter and submillimeter wavelength ranges. The results of dynamic measurements show that in these junctions the superconducting current exhibits a sinusoidal dependence on the phase difference of the superconducting wave functions of the electrodes, and a simple resistive model is used to analyze their microwave properties. At the same time, the temperature dependence of the critical current of the junctions differs appreciably from that typical of tunnel junctions with s-superconductors and may be explained as d-type pairing of the superconducting electrodes and an SNS junction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1262444
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  • 2
    Electronic Resource
    Electronic Resource
    Phase dependence of the superconducting current in YBCO Josephson junctions on a bicrystal substrate (1999)
    Springer
    Technical physics letters 25 (1999), S. 913-916 
    Details
    ISSN: 1090-6533
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Dependences of the amplitudes of the harmonic and subharmonic Shapiro steps on an external monochromatic signal were used to study the current-phase dependence of high-temperature superconducting junctions on a bicrystal substrate. It is shown that for a symmetric definition of the transport current across the junction with an edge transparency of the order of $$\bar D = 10^{ - 4}$$ and a mirror-symmetric bicrystal interface, the current-phase dependence is close to sinusoidal which differs from the theoretical predictions and is most likely caused by twinning of the high-temperature superconducting films of the electrodes forming the junction. A departure from symmetry in the definition of the transport current across the junction causes the current-phase dependence to deviate from sinusoidal, which increases with increasing degree of asymmetry. This change in the current-phase dependence is accurately described by a model which takes into account the formation of coupled Andreev states in junctions of superconductors with a $$d_{x^2 - y^2 } $$ type of superconducting wave function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1262682
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  • 3
    Electronic Resource
    Electronic Resource
    Transport properties of Tl2Ba2CaCu2O8 weak links on LaAlO3 bicrystal substrates (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9221-9223 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson junctions and dc superconducting quantum interference devices (SQUIDs) have been fabricated in ex situ epitaxial Tl2Ba2CaCu2O8 films on bicrystal LaAlO3 substrates with symmetric 32° [001] tilt grain boundaries. The critical temperature Tc, of the junctions was in the range 105–107 K and the critical current densities at 77 K varied between 3×102 and 3×104 A/cm2, two or three orders of magnitude less than those of the film. The I–V curves are described by a resistively shunted junction model. Close to Tc, the temperature dependence of the critical current was described by (1−T/Tc)2. The flux noise spectra SΦ(f) of dc SQUIDs were measured in the locked-loop regime with constant current bias at temperatures up to 94 K. The white noise level was 50μΦ0/(square root of)Hz at 77 K. The crossover frequency to 1/f noise was low, about 5 Hz, and the flux noise level at 1 Hz was 440μΦ0/(square root of)Hz. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362595
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  • 4
    Electronic Resource
    Electronic Resource
    YBa2Cu3O7−x films on yttria-stabilized ZrO2 substrates: Influence of the substrate morphology (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7958-7965 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: c-axis-oriented YBa2Cu3O7−x (YBCO) thin films were laser deposited on (001) yttria-stabilized ZrO2 (YSZ) substrates with different surface morphologies. The in-plane orientation of the films on smooth substrates was sensitive to the deposition conditions, often resulting in mixed orientations. However, a strongly dominating [110]YBCO//[110]YSZ orientation was obtained at a deposition temperature of 770 °C. Films on substrates with surface steps, induced by depositing a homoepitaxial buffer layer or by thermally annealing the substrate, had a [110]YBCO//[100]YSZ orientation when deposited at the same temperature. It was concluded that the [110]YBCO//[100]YSZ orientation was promoted by a graphoepitaxial mechanism. Films prepared under identical conditions on smooth and stepped substrates grew with extended c axes on the former. It is proposed that the extension can be induced by disorder, invoked by a low oxygen pressure and a low density of adsorption sites. The disorder may be eliminated by either an increase of the oxygen pressure or an increase of the density of adsorption sites in the form of steps. The film microstructure influenced the microwave surface resistance, which was similar for films with one exclusive in-plane orientation and higher for films with mixed orientations. The films on the stepped surfaces had superior superconducting properties; inductive measurements gave a Tconset of 88 K, a ΔT(90%–10%)c of 0.2 K, and the transport jc was 1.5×106 A/cm2 at 83 K, for films on substrates with homoepitaxial buffer layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356557
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  • 5
    Electronic Resource
    Electronic Resource
    Bicrystal junctions and superconducting quantum interference devices in YBa2Cu3O7 thin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7972-7977 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson junctions and superconducting quantum interference devices (SQUIDs) were made by depositing thin films of YBa2Cu3O7 on bicrystal substrates of Y-ZrO2 and SrTiO3. The critical current density of the junctions at 77 K could be adjusted from 100 to 106 A/cm2 by selecting bicrystals with misorientation angles θ from 45° to 0°. Current-voltage curves from junctions with θ(approximately-greater-than)22° followed the resistively shunted junction model with noise rounding close to the transition temperature. The response of the critical current to magnetic fields was Fraunhofer-like and the width (w) dependence was 1/w2 due to flux focusing effects. Shapiro steps under microwave radiation were observed. SQUIDs based on these junctions had energy resolutions at 77 K down to 8.6×10−30 J/Hz and a 10 Hz flux noise level down to 1.5×10−9 Φ20/Hz at 85 K. A SQUID of the Ketchen design with a flux focusing washer had a magnetic field sensitivity of 15 pT/(square root of)Hz at 77 K. The temperature dependence of the voltage modulation depth close to TC was examined and found to be in agreement with theory [K. Enpuku, Y. Shimomura, and T. Kisu, J. Appl. Phys. 73, 7929 (1993)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356559
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  • 6
    Electronic Resource
    Electronic Resource
    Novel design of rapid single flux quantum logic based on a single layer of a high-Tc superconductor (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 138-140 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We suggest a new design of rapid single flux quantum (RSFQ) logic circuits which is based on a single superconducting layer and does not require a superconducting ground plane. Small inductances of about 10 pH, obligatory for RSFQ circuits, are formed as narrow slits of widths comparable to the London penetration depth ((approximately-equal-to)0.15 μm). The design allows us to decrease the geometric size of the RSFQ cell. Test circuits with YBaCuO grain boundary junctions on asymmetric 32° Y– ZrO2 bicrystals were used to measure the slit inductance per unit length and the mutual inductance of neighboring slits. A typical inductance of a 0.4 μm slit was found to be 0.7–0.8 pH/μm. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115472
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  • 7
    Electronic Resource
    Electronic Resource
    Voltage divider based on submicron slits in a high Tc superconducting film and two bicrystal grain boundaries (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 282-284 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments on a model of rapid single flux quantum (RSFQ) flip-flop cell, based on high-Tc (HTS) Josephson junctions show that it can operate as a voltage divider at frequency up to 400 GHz. The junctions were formed in YBaCuO film, deposited on novel Y–ZrO2 bicrystals with two asymmetric 32° grain boundaries, about 10 μm apart, and allow a new design of RSFQ logic based on a single HTS layer. Small inductances ((approximately-equal-to)10 pH) were made as narrow, submicron size slits. The junction widths were between 4 and 10 μm and for ten junctions located close to the tested circuits, the linear critical current densities at T=4.4 K were 10.7 μA/μm±50% for one grain boundary and 8.3 μA/μm±50% for the other one. IcRn was about 1 mV±50%. A current density of half the expected value meant that the test circuit did not act as an ideal flip–flop down to the lowest frequency. As a voltage divider it gave a half value division up to 0.82 mV at T=4.4 K and to 0.4 mV at 30 K. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114783
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  • 8
    Electronic Resource
    Electronic Resource
    100 GHz oscillations on monolithic high Tc chip (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 896-898 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have coupled 80–180 GHz oscillations from a HTc Josephson junction onto an on-chip YBa2Cu3O7/SiO/Au microstrip resonator. Efficient coupling was achieved at the resonance frequencies and both resonance frequency and Q value could be measured from the I-V curve. The use of a superconductor in the microstrip gave negligible dispersion (〈4%) from 80 to 180 GHz, whereas the attenuation of 4–8 dB/nm originated mainly from the normal metal groundplane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108559
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  • 9
    Electronic Resource
    Electronic Resource
    Low 1/f noise in YBa2Cu3O7 dc SQUIDs on (Y)ZrO2 bicrystal substrates (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 861-863 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report low noise operation of YBa2Cu3O7 SQUIDs superconducting quantum interference devices using Josephson junctions grown on bicrystal substrates of (Y)ZrO2. Energy sensitivities measured at 10 Hz (Sε=4.5×10−29 J/Hz) were to our knowledge lower than previously reported for a YBa2Cu3O7 SQUID with practical loop size (∼40 μm). The 1/f part of the voltage noise reached a maximum at 85 K where the noise spectrum was essentially white. The 1/f noise increased both at lower temperatures due to increased critical current fluctuations (∼Ibias2.2) and at higher temperatures, where the flux noise from the film produces a peak below Tc(=89 K).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107769
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  • 10
    Electronic Resource
    Electronic Resource
    Weak links and dc SQUIDS on artificial nonsymmetric grain boundaries in YBa2Cu3O7−δ (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 3030-3032 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied weak links and dc–SQUIDs made from pulsed laser deposited YBa2Cu3O7−δ thin films on Y–ZrO2 bicrystal substrates. The transport properties of the weak links were studied as a function of the misorientation angle (θ) between the two halves of the bicrystal and an exponential dependence of the weak link critical current density was observed for angles up to 40° at 77 K. Josephson effects with clear microwave and magnetic field responses were observed. An optimum dc–SQUID performance at 77 K was obtained for θ=32°. At this temperature, we achieved a periodic magnetic field response with a modulation depth of 12 μV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105783
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