Interface-engineered Josephson-Kontakte
Interface-engineered Josephson-Kontakte
The Josephson junction is the key active device in the superconductor electronics. Junctionsin the ramp-edge geometry provide the most flexible type, since the specific junction propertiescan be adjusted by the material and thickness of the barrier layer. Furthermore, they arecompatible to a multila...
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Personal Name(s): | Heinsohn, Jan-Klaas (Corresponding author) |
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Contributing Institute: |
Publikationen vor 2000; PRE-2000; Retrocat |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2000
|
Physical Description: |
III, 172 p. |
Document Type: |
Report Book |
Research Program: |
ohne Topic |
Series Title: |
Berichte des Forschungszentrums Jülich
3828 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
The Josephson junction is the key active device in the superconductor electronics. Junctionsin the ramp-edge geometry provide the most flexible type, since the specific junction propertiescan be adjusted by the material and thickness of the barrier layer. Furthermore, they arecompatible to a multilayer technology, enabling them for integrated-circuit applications. Inthis work, a new type of Josephson junction in the ramp-edge geometry made of the hightemperaturesuperconductor YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) was investigated. In the "interface-engineered"junctions a natural barrier is formed by treatment of the ramp interface instead ofdepositing an artificial, non-superconducting barrier layer.The first part of the work describes the optimization of the several parts of the process and theinvestigation of the significant process parameters as well as their physical meaning. By applicationof statistical methods in the design and analysis of the experiments, potentially importantfactors and additionally their interactions could be examined thoroughly. A processwas developed that yields Josephson junctions with reproducible properties which can bedescribed by the "resistively and capacitively shunted junction" (RCSJ) model. The criticalcurrent densities and the normal resistances of these junctions cannot be strongly influencedby the conduction of the process. However, a Lanthanum doping of the superconductor leadsto a large variation of the parameters above a threshold La-concentration of about 5%.The investigation of the transport properties of the junctions forms the second part of thiswork. Measurements of the current-voltage characteristics with and without microvave irradiationand the behavior in a magnetic field demonstrate the RCSJ-similarity of the junctions aswell as the homogeneity of the current transport through the barrier. The dependence of themagnetic-field modulation of the critical current on the orientation of the magnetic fieldshows that the current flow in ramp-type junctions takes place parallel to the electrodes andnot perpendicular to the barrier. Furthermore, these measurements give insight in the way themagnetic field penetrates the junctions and hint on a general sensitivity of the ramp-edge geometrywith respect to flux trapping. By investigating the temperature dependence of thejunction parameters a qualitative model of the barrier in the interface-engineered junctionscould be developed which consistently describes both the quasiparticle and the Cooper-pairtransport in a so-called ScNS model. The barrier consists of an isolator containing localizedstates and microshorts, followed by a superconductor with reduced critical temperature. Thejunctions made of La-doped YBCO exhibit a more homogeneous distribution and reduceddiameter of the microshorts. |