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  • 1
    Electronic Resource
    Electronic Resource
    Ultraviolet light assisted oxygenation process for submicron YBa2Cu3O7−δ thin film devices (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5411-5418 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have successfully fabricated superconducting nanobridges and grain-boundary junctions from epitaxial YBa2Cu3O7−δ thin films with thickness between 20 and 30 nm and width down to ∼100 nm. The patterning process turned out to severely deteriorate the transport properties resulting in structural damage, corrosion, and oxygen loss. The most crucial steps are the baking procedure used to cure the electron beam resist, the resist development, and the ion beam etching process. By optimizing these steps and applying a suitable post-treatment procedure a significant enhancement of the sample quality could be achieved. An ultraviolet light assisted oxygenation procedure after the patterning process enabled us to achieve superconducting transition temperatures between 80 and 87 K and critical current densities at 4.2 K up to 4×107 A cm−2 for the nanobridges and 5×103–2×105 A cm−2 for the grain boundary junctions. At 4.2 K junctions with width down to 100 nm corresponding to a junction area down to 2.3×10−3 μm2 showed superconductivity. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459599
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  • 2
    Electronic Resource
    Electronic Resource
    Correlation of critical current and resistance fluctuations in bicrystal grain boundary Josephson junctions (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1929-1931 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed a detailed analysis of the low frequency 1/f noise in YBa2Cu3O7−δ and Bi2Sr2CaCu2O8+x grain boundary Josephson junctions (GBJs) fabricated on SrTiO3 bicrystal substrates. The normalized fluctuation of the critical current, δIc/Ic, and the normal resistance, δRn/Rn were found to be almost independent of temperature and the misorientation angle. Furthermore, the magnitude of the fluctuations is very similar for both high-Tc cuprates. Correlation experiments showed that the fluctuations of Ic and Rn are anti-correlated. Our analysis strongly suggests that the source of 1/f noise in high-Tc bicrystal GBJs are localized defect states in an insulating grain boundary barrier with fluctuating electron occupation. The effective charge trapping time within single traps was found to decay exponentially with increasing bias voltage. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114571
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  • 3
    Electronic Resource
    Electronic Resource
    Comparison of Josephson vortex flow transistors with different gate line configurations (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1095-1097 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We performed numerical simulations and experiments on Josephson vortex flow transistors based on parallel arrays of YBa2Cu3O7–δ grain boundary junctions with a cross gate line allowing us to operate the same devices in two different modes named the Josephson fluxon transistor (JFT) and Josephson fluxon–antifluxon transistor (JFAT). The simulations yield a general expression for the current gain versus number of junctions and normalized loop inductance and predict higher current gain for the JFAT. The experiments are in good agreement with simulations and show improved coupling between gate line and junctions for the JFAT as compared to the JFT. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1346625
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  • 4
    Electronic Resource
    Electronic Resource
    On the nature of the electric-field effect on YBa2Cu3O7−δ grain boundary junctions employing epitaxial SrTiO3 gate insulators (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1027-1029 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated Josephson field-effect transistors based on YBa2Cu3O7−δ bicrystal grain-boundary junctions (GBJs) and epitaxial SrTiO3 films as gate insulators. The SrTiO3 gate insulator shows high products of the breakdown field Ebd and the dielectric constant εr up to Ebdεr=1.3×1010 V/m allowing measurements over a wide range of applied gate electric-field Eg. The critical current Ic of the GBJs is found to depend highly nonlinear on Eg. Remarkably, the measured Ic(Eg) are very similar to the εr(Eg) curves. This strongly suggests that the observed electric-field effect is not due to a field-induced change in carrier concentration but is related to the dielectric properties of the SrTiO3 gate insulator. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123444
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  • 5
    Electronic Resource
    Electronic Resource
    Strain effects and microstructure of epitaxial manganite thin films and heterostructures (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3636-3638 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have grown epitaxial La2/3Sr1/3MnO3 (LSMO) and La2/3Ba1/3MnO3 (LBMO) thin films as well as La2/3Ba1/3MnO3/SrTiO3 heterostructures by pulsed-laser deposition. The microstructure of the films was analyzed by x-ray diffraction and transmission electron microscopy. A significant effect of strain due to lattice mismatch was found. Whereas the thick LBMO films show perfect epitaxy and grow coherently strained over the full film thickness, the LSMO films were found to be composed of two layers separated by an intrinsic interface region containing a high density of defects. The approximately 60 nm thick bottom layer grows coherently on the SrTiO3 (STO) substrate and is highly strained, whereas the top layer is almost strain free. The LBMO/STO heterostructures are coherently strained and show a very low density of defects and sharp interfaces. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123206
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  • 6
    Electronic Resource
    Electronic Resource
    Low temperature scanning electron microscopy study of YBa2Cu3O7−δ multilayer dc SQUID magnetometers (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1555-1557 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low temperature scanning electron microscopy (LTSEM) has been used to analyze the superconducting properties of integrated magnetometers involving a dc superconducting quantum interference device. The study yielded spatially resolved information on the critical temperature Tc and critical current density Jc in the upper and lower superconducting layers of the YBa2Cu3O7−δ/SrTiO3/YBa2Cu3O7−δ structure. The Tc of the lower film was depressed by several kelvin, and the Jc of the upper film was lower where it crossed the edge of a lower YBa2Cu3O7−δ film covered with SrTiO3. A gradient in Tc was observed in the lower film near the edge of a via, arising presumably from oxygen diffusion during fabrication. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115697
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  • 7
    Electronic Resource
    Electronic Resource
    Asymmetric high temperature superconducting Josephson vortex-flow transistors with high current gain (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1010-1012 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated Josephson vortex-flow transistors (JVFTs) based on asymmetric parallel arrays of YBa2Cu3O7−δ bicrystal grain boundary junctions. The critical current Ic and the voltage V at fixed bias current Ib were measured as a function of the control current Ictrl through a control line inductively coupled to the array. For JVFTs with an asymmetric in-line geometry a high current gain g=∂Ic/∂Ictrll ranging between about 20 at 40 K and 14 at 70 K was achieved. This current gain is much higher than that obtained for symmetric devices and results from the self-field effect of the electrode currents. In contrast to the current gain the transresistance rm=∂V/∂Ictrl of the JVFTs could not be enhanced by an asymmetric device structure. The current-voltage characteristics of the asymmetric JVFTs show pronounced step-like structures caused by the self-field of the electrode currents. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114713
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  • 8
    Electronic Resource
    Electronic Resource
    Superconducting Nd1.85Ce0.15CuO4−y bicrystal grain boundary Josephson junctions (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2888-2890 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the electric transport properties of symmetrical [001] tilt Nd1.85Ce0.15CuO4−y (NCCO) bicrystal grain boundary Josephson junctions (GBJs) fabricated on SrTiO3 bicrystal substrates with misorientation angles of 24° and 36.8°. The superconducting properties of the NCCO GBJs are similar to those of GBJs fabricated from the hole doped high temperature superconductors (HTS). The critical current density Jc decreases strongly with increasing misorientation angle. The products of the critical current Ic and the normal resistance Rn (∼100 μV at 4.2 K) are small compared to the gap voltage and fit well to the universal scaling law IcRn∝Jc found for GBJs fabricated from the hole doped HTS. This suggests that the symmetry of the order parameter, which most likely is different for the electron and the hole doped HTS, has little influence on the characteristic properties of symmetrical [001] tilt GBJs. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121449
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  • 9
    Electronic Resource
    Electronic Resource
    Scaling behavior of 1/f noise in high-temperature superconductor Josephson junctions (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 120-122 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extensive studies of the low frequency 1/f noise in high-temperature superconducting (HTS) Josephson junctions of various types and materials have been performed for a wide range of operating parameters. The origin of the measured voltage fluctuations can be traced back to the trapping and release of charge carriers in trapping centers in an insulating barrier, giving rise to correlated fluctuations of the junction critical current Ic and normal-state resistance Rn. We observed a linear dependence of the normalized critical current and resistance fluctuations on Rn, which suggests a constant density of trapping centers for the HTS Josephson junctions. The scaling of the normalized fluctuations is in good agreement with the previously found scaling relation IcRn∝1/Rn and supports a junction model assuming a leaky tunnel barrier. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119281
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  • 10
    Electronic Resource
    Electronic Resource
    La1.85Sr0.15CuO4−δ bicrystal grain boundary Josephson junctions (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3341-3343 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated La1.85Sr0.15CuO4−δ grain boundary Josephson junctions (GBJs) fabricated on [001] tilt SrTiO3 bicrystals with misorientation angles of 24° and 36.8°. The resistive transition and the current–voltage characteristics of the GBJs are found to be close to those predicted by the resistively shunted junction (RSJ) model. Their product of the critical current density, Jc, and the normal resistance times area ρn, scales proportional to about (Jc)q with q=0.5–0.6 similar to what is found for YBa2Cu3O7−δ GBJs. By analyzing Fiske resonances the Swihart velocity of the GBJs and the ab-plane London penetration depth of La1.85Sr0.15CuO4−δ are obtained to c¯=2.5×106 m/s and λL=200 nm at 4.2 K, respectively. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116051
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