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  • 1
    Electronic Resource
    Electronic Resource
    Response of YBaCuO thin-film microbridges to microwave irradiation (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1368-1370 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microbridges with widths of about 10 μm were lift-off structured from rf-sputtered YBaCuO thin films and irradiated with microwaves at different temperatures. The bridges contain only a few grains with a typical size of 4 μm and are fully c-axis oriented. The observed current-voltage characteristics exhibit sharp constant voltage steps up to 71 K. An oscillatory dependence of the critical current I0 and the step heights 2In is observed, clearly revealing Josephson-like behavior. From the grain structure, the critical current, and the microwave response, it is very likely that grain boundaries as superconductor-normal conductor-superconductor (SNS) contacts dominate the behavior of the bridges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101403
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  • 2
    Electronic Resource
    Electronic Resource
    YBa2Cu3Ox/PrBa2Cu3Ox/YBa2Cu3Ox Josephson ramp junctions (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 575-583 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed study of the fabrication process, current voltage (I-V) characteristics, and Josephson and normal-state properties of the YBa2Cu3Ox(YBCO)/PrBa2Cu3Ox(PBCO)/YBCO ramp junctions is presented. The I-V characteristics can be well described by the resistively shunted junction model. It was found that the critical current Ic and the normal-state conductance 1/Rn scale linearly with the junction area, whereas Ic, the excess current Iex, and IcRn products decrease with increasing barrier thickness. These junctions with cross-sectional area A have a good controllability, low capacitance, and high values of IcRn and RnA products. The coherence length ξn of the PBCO barrier is estimated to be between 5 and 8 nm. As unambiguous evidence of the Josephson behavior, the microwave response as a function of the microwave power as well as the modulations of critical current Ic(H) with applied magnetic field are shown. A modulation depth of more than 95% has been observed. Small proximity effect parameters and junction capacitance (C/A∼10−7 F/cm2) show an advantage of these junctions for many applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351835
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  • 3
    Electronic Resource
    Electronic Resource
    Noise study of a high-Tc Josephson junction under near-millimeter-wave irradiation (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 927-929 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Noise studies of both the dc and ac Josephson effects have been performed on a high-Tc ramp-type Josephson junction irradiated at 176 GHz. Well-established analytical results for noise in overdamped RSJs are used to model the measured I-V characteristics, and their agreement is excellent. Noise-rounded I-V curves at the critical current and the first and second Shapiro steps under coherent 176 GHz radiation have been studied in detail at several temperatures and rf power levels. The noise temperatures inferred from these simulations are close to the physical temperatures. An increase of noise temperatures at high radiation power levels is a result of radiation heating, which could be due to a bolometric effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110974
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  • 4
    Electronic Resource
    Electronic Resource
    Epitaxial YBa2Cu3Ox thin films on sapphire with a PrBa2Cu3Ox buffer layer (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2333-2337 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Highly c-axis-oriented YBa2Cu3Ox thin films have been grown on (11¯02) sapphire substrates by a modified off-axis magnetron rf-sputtering technique. To prevent the interaction and to improve the lattice match between film and substrate a thin layer of 10–60 nm of PrBa2Cu3Ox was used as a buffer layer. The diffusion process was effectively blocked and the epitaxy was enhanced. The Jc (77 K) has been measured to be 4×105 A/cm2 which is significantly higher than the Jc of films directly grown on Al2O3 (∼8×104 A/cm2). The surface resistance of such films at 11 GHz and 4.2 K was measured to be 80 μΩ for 50-nm thin films. These results are comparable to the best results reported so far on sapphire with other buffer layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351086
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  • 5
    Electronic Resource
    Electronic Resource
    (305) SrTiO3 as substrate for coherently tilted epitaxial YBa2Cu3Ox thin films (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 607-609 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High Tc superconducting YBa2Cu3Ox (YBCO) thin films have been prepared on (305) SrTiO3 (STO) substrates. X-ray diffraction analysis and Rutherford backscattering experiments reveal that the c-axis of the layers is directed along the [001] STO axis. Bragg reflection measurements from YBCO lattice planes with high h, k, and l indices confirm that the film growth is epitaxial and almost single domain. For the critical current density jc(77 K) values of 2×106 and 1×103 A/cm2 have been found in the [010] and [501¯] YBCO directions, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107851
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  • 6
    Electronic Resource
    Electronic Resource
    Ramp-type junction parameter control by Ga doping of PrBa2Cu3O7−δ barriers (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 848-850 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We analyzed the transport of charge carriers across PrBa2Cu3−xGaxO7−δ (PBCGO) barriers as a function of barrier thickness, Ga-doping level, temperature, and bias voltage. It was found that by Ga doping, the normal state resistance (Rn) of the junctions was systematically increased, while the critical current (Ic) remained constant. We argue that pair transport takes place by direct tunneling, whereas the quasiparticles have access to channels formed by one or more localized states inside the barrier. By Ga doping the IcRn products were increased, up to 8 mV at 4.2 K for junctions with 8 nm thick PrBa2Cu2.6Ga0.4O7−δ barriers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117912
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  • 7
    Electronic Resource
    Electronic Resource
    CeO2 as insulation layer in high Tc superconducting multilayer and crossover structures (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 553-555 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a study of the electrical properties of insulating CeO2 layers in combination with superconducting (Y/Dy) Ba2Cu3O7−δ (RBCO) films over ramps and in crossover structures. CeO2 is frequently used as a buffer layer, or template layer for biepitaxial grain boundary junctions, but can also be used as an insulating layer in ramp-type junctions and other multilayer structures. Epitaxial thin films of CeO2 were deposited by pulsed laser ablation using SrTiO3 substrates. We characterized the insulating performance of CeO2 thin films in terms of breakdown field Ebd and the relative dielectric constant εr. For 80 nm thick CeO2 at 77 K we found Ebd=1×106 V/cm, using a 1 nA/100 μm2 breakdown criterion, which gives us a specific resistivity of ρ≥109 Ω cm up to breakdown. From capacitance measurements on planar RBCO/CeO2/RBCO structures we obtained for the dielectric constant: εr≈15. The texture of CeO2 in combination with RBCO on ramped surfaces, simulated by SrTiO3 (STO) (103) substrates having their normal tilted by 18° away from the STO[001] direction, has been studied by x-ray diffraction. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116397
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  • 8
    Electronic Resource
    Electronic Resource
    Near-millimeter-wave response of high Tc ramp-type Josephson junctions (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3351-3353 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the response of a YBCO/PBCO/YBCO ramp-type junction to coherent radiation at 176 and 270 GHz. The I-V characteristic of the junction closely resembles the prediction of the RSJ model. The IcRn product of the junction is 0.25 mV at 5 K. The millimeter-wave radiation is coupled to the junction via a quasioptical structure that focuses the radiation onto the junction through a yttrium-stabilized ZrO2 substrate. At 176 GHz, we have observed as many as six Shapiro steps at the maximum power level of our Gunn oscillator-pumped frequency doubler. Shapiro steps are still clearly seen up to 65 K. The amplitudes of the zeroth, first, and second Shapiro steps, as functions of the square root of the radiation power, agree remarkably well with a Bessel function fit, indicating the junction is voltage-biased at the radiation frequency (rf). At 270 GHz, due to a combination of the heavy rf loss in the ZrO2 substrate and the lack of radiation power, we have observed only the first Shapiro step.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109068
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  • 9
    Electronic Resource
    Electronic Resource
    Nucleation and growth of PrBa2Cu3O7−δ barrier layers on ramps in DyBa2Cu3O7−δ studied by atomic force microscopy (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1276-1278 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We studied the microstructure of Ar ion-beam etched ramps in epitaxial DyBa2Cu3O7−δ films by atomic force microscopy. Generally, ramps were well aligned (φ≈0°) with one of the crystal axes of the (001) SrTiO3 substrate. In those cases we observed a surface reconstruction into a regular pattern of very long (up to 0.5 μm), about 20 nm wide facets, parallel to the ramp edge. For high misorientation angles (φ(approximately-greater-than)0°), the reconstruction appeared much more complex and less regular. Furthermore, we investigated the nucleation and growth of very thin barrier layers of PrBa2Cu3O7−δ on well aligned ramps. We found that nucleation takes place in the shallow trenches in the ramp, where facets meet. When more material is deposited, islands coalesce to form closed domains parallel to the trenches. This causes a thickness modulation close to 100% for barrier layer thickness up to 6 nm. The conclusions drawn from this research allow for an important improvement of the technology for the fabrication of ramp-type junctions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115951
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  • 10
    Electronic Resource
    Electronic Resource
    Characteristics of advanced YBa2Cu3Ox/PrBa2Cu3Ox/YBa2Cu3Ox edge type junctions (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2754-2756 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This letter describes the scaling behavior and Josephson properties of improved YBCO/PBCO/YBCO edge-type junctions. The critical current, normal-state resistance, and IcRn product scale with barrier thickness and junction area. The coherence length of the PBCO barrier is estimated to be between 5 and 8 nm. As unambiguous evidence of the Josephson behavior, the microwave response as a function of microwave power, as well as the current modulation with applied magnetic field, have been studied: well-developed Shapiro steps at 10 GHz have been observed, and the modulation of Ic(H) shows Fraunhofer-like behavior with 95% Ic suppression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105878
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