Publications (7)44.5 Total impact
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Article: Current distribution in a planar YBa2Cu3O7-δ multiline structure
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ABSTRACT: The characterization of the current density distribution in an edge-shaped region of a planar YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> flux transformer is reported for the first time. The analysis was performed by means of three-dimensional computation of the electromagnetic field. In addition, experimental studies using low-temperature scanning electron microscopy were carried out. It is shown that the current density distribution in edge regions deviates strongly from the symmetric case, which is established in the case of straight conductors. The results of calculation and measurement are discussed with respect to consequences for the design of flux transformers for SQUID systemsIEEE Transactions on Magnetics 02/1995; · 1.36 Impact Factor -
Article: Spatially resolved analysis of high‐Tc grain boundary Josephson junctions and arrays
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ABSTRACT: Using Low Temperature Scanning Electron Microscopy (LTSEM) we have studied the spread of the critical current values in one‐ and two‐dimensional arrays of high‐T c grain boundary Josephson junctions (GBJs). For series arrays the critical current values and the magnetic field dependences of all GBJs within the array could be imaged by LTSEM. Our measurements showed that part of the spread of the critical current values derived from measurements of the current‐voltage characteristics is caused by variations of the local magnetic field at the junction position. For bicrystal GBJs a Gaussian distribution of the critical current values with a spread as small as ±20% was found. For the investigated step‐edge and biepitaxial GBJs the spread of the critical current values was considerably larger. The LTSEM technique also was used to study the spatial homogeneity of the critical current density of the different types of YBa 2 Cu 3 O 7-δ grain boundary Josephson junctions with a spatial resolution of 1μm. Whereas the critical current density of bicrystal GBJs showed only small variations on this length scale, strong inhomogeneities were found for step‐edge and biepitaxial GBJs. © 1994 American Institute of Physics.Journal of Applied Physics 01/1995; · 2.17 Impact Factor -
Article: Spatially Resolved Observation of Static Magnetic Flux States in YBa2Cu3O7-dgr Grain Boundary Josephson Junctions.
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ABSTRACT: With low-temperature scanning electron microscopy, the magnetic flux states in high critical temperature Josephson junctions have been imaged. The experiments were performed with YBa(2)Cu(3)O(7-delta) thin-film grain boundary Josephson junctions fabricated on [001] tilt SrTiO(3) bicrystals. For applied magnetic fields parallel to the grain boundary plane, which correspond to local maxima of the magnetic field dependence of the critical current, the images clearly show the corresponding magnetic flux states in the grain boundary junction. The spatial modulation of the Josephson current density by the external magnetic field is imaged directly with a spatial resolution of about 1 micrometer.Science 03/1994; 263(5150):1112-4. · 31.20 Impact Factor -
Article: Distribution of the critical current density and flux trapping in YBa2Cu3O7-δ ramp‐edge Josephson junctions
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ABSTRACT: We have studied the spatial distribution of the critical current density in YBa 2 Cu 3 O 7-δ ramp edge Josephson junctions using low‐temperature scanning electron microscopy. Applying this technique allows the imaging of the critical current density distribution with a spatial resolution of about 1 μm. Our measurements show that the geometry of the ramp‐edge junction eases the trapping of magnetic flux quanta in the YBa 2 Cu 3 O 7-δ layer covering the ramp edge. These trapped flux quanta result in a spatially inhomogeneous magnetic field parallel to the barrier layer, which in turn results in a spatially modulated supercurrent density and an unusual magnetic field dependence of the critical current.Applied Physics Letters 02/1994; · 3.84 Impact Factor -
Article: Spatially resolved electrical characterization of a YBa2Cu3O7-δ flux transformer
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ABSTRACT: We report the spatially resolved transport properties of a three‐layer YBa 2 Cu 3 O 7-δ flux transformer using low‐temperature scanning electron microscopy. The seven‐turn spiral coil is fabricated using a crossover technology with SrTiO 3 as an insulator. The different layers were patterned with shadow masks or optical lithography. We show that the insulating SrTiO 3 film has no shorts and that the overlaying YBa 2 Cu 3 O 7-δ spiral reveals a reduced zero resistance critical temperature at the steps and edges of the insulator.Applied Physics Letters 06/1993; · 3.84 Impact Factor -
Article: Very high critical current densities in YBa2Cu3 O7-δ/Nd1.83Ce0.17CuOx superlattices
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ABSTRACT: The critical current density of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub>/Nd<sub>1.83</sub>Ce <sub>0.17</sub>CuO<sub>x</sub> (Y/Nd) superlattices grown heteroepitaxially by hollow cathode magnetron sputtering was measured in magnetic fields perpendicular and parallel to the c -axis. The thickness d <sub>Y</sub> and d <sub>Nd</sub> of the individual Y and Nd layers ranged between 50 and 400 Å. In superlattices with modulation periods below a critical wavelength Λ<sub>c</sub>=450 Å the Y layers are coherently strained, whereas in those with modulation periods above Λ<sub>c</sub> the coherency strain starts to relax, resulting in the formation of a high density of misfit dislocations. Very high zero field critical current densities up to 1.1×10<sup>7</sup> A/cm<sup>2</sup> were observed for multilayers with a modulation period just above Λ<sub>c</sub>. For B perpendicular to the c -axis, the critical current density J <sub>c⊥ </sub> is almost independent at B up to a certain field (≈2 T for d <sub>y</sub>=100 Å) that corresponds to the lower critical field of the Y layers. J <sub>c⊥</sub> values as high as 2×10<sup>6</sup> A/cm<sup>2</sup> were obtained for B =1 T and T =77 K. The angular dependence J <sub>c </sub>(φ) is determined solely by the magnetic field component parallel to the c -axis demonstrating the two-dimensional nature of the superlatticesIEEE Transactions on Appiled Superconductivity 04/1993; · 1.04 Impact Factor -
Article: Superconducting transport properties of step-edge Josephson junctions
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ABSTRACT: The electrical transport properties of YBa<sub>2</sub>Cu<sub>3 </sub>O<sub>7-δ</sub> step-edge junctions (SEJs) fabricated on step edges in (100) SrTiO<sub>3</sub> substrates have been investigated. In particular, the influence of the step angle and the ratio of the step height and the film thickness on the superconducting properties of the junctions were studied. Steps of different height and angle were patterned into (100) SrTiO<sub>3</sub> substrates by ion beam etching (IBE). Epitaxial YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> films were grown on these substrates by sputtering and patterned by IBE. The samples were characterized by four-probe electrical measurements. The critical current density of the SEJs was found to depend strongly on the ratio of the step height to the film thickness. The critical current density distribution of the SEJs was imaged by low-temperature scanning electron microscopy and was found to be strongly inhomogeneousIEEE Transactions on Appiled Superconductivity 04/1993; · 1.04 Impact Factor
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Institutions
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1993
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Eberhard-Karls-Universität Tübingen
Tübingen, Baden-Wuerttemberg, Germany
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