Fluxon propagation on long Josephson junctions
Wave propagation on superconductive strip transmission lines which incorporate Josephson tunneling along the length is discussed. Attention is primarily focused on fluxon propagation and its effects on the volt-ampere characteristics of the Josephson junctions. Analytical solutions, computer simulations, and a mechanical model are used to explain the experimental measurements on long junctions. These devices were fabricated using niobium and lead superconductors with a niobium oxide barrier formed by RF or thermal oxidation. Experimental measurements of the dc Josephson current show that in most practical cases, this current is concentrated near the boundaries of the junctions. This causes the junction to switch prematurely to a dynamic state by admitting fluxons from the edges. Consequently, long Josephson junctions, regardless of their geometries, support dc Josephson currents which are usually much less than values predicted using uniform current distribution. The current singularities, at well defined voltages, on the volt-ampere characteristics of the Josephson junctions are due to resonant propagation of fluxons. It is shown that, for proper bias conditions, a fluxon may be reflected back, not as one antifluxon but several. Over a period, a certain number of fluxons propagate in one direction in part of the cycle and a different number of antifluxons propagate in the opposite direction in the remainder of the period. These additional asymmetric modes result in steps centered between the previously known steps of the volt-ampere characteristics.
- Research Organization:
- Wisconsin Univ., Madison (USA)
- OSTI ID:
- 6478737
- Country of Publication:
- United States
- Language:
- English
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