Probing d-c Josephson current distributions
Thesis/Dissertation
·
OSTI ID:6023552
The d-c Josephson current distributions of tunnel junctions have been studied. To probe the local current density, a focused weak laser beam was used as a local heat source on the junction to perturb the current density in a small region. This perturbation resulted in a small variation in the maximum zero-voltage current. As the laser beam was scanned the maximum zero-voltage current's variation was recorded as a function of beam position. Using this technique junctions of several geometries were studied under a variety of conditions including various external magnetic fields, current feed, and L/lambda/sub J/ ratios, where L is the length of the junction and lambda/sub J/ is the Jospehson penetration depth. For the first time direct comparison between experimentally-measured distributions and theory have been made. Distributions for one-dimensional junctions were first examined. In the absence of external magnetic field, long junctions exhibit non-uniform distributions as result of self-generated magnetic fields, while shorter junctions displayed a more uniform distribution. In applied fields, stationary vortex structures were observed. The observations were found to be in good agreement with theory. The technique was extended to study two-dimensional junctions, where theory was obscure. The experimentally observed distributions were found to be contrary to the published theoretical distributions. Using a new method of theoretical calculations, the Josephson current distributions were found for one-dimensional junctions and two-dimensional junctions. There was good agreement between these distributions and experimental distributions. Also this calculation method was used to model the laser perturbation of the current distribution.
- OSTI ID:
- 6023552
- Country of Publication:
- United States
- Language:
- English
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