| 摘要 |
PURPOSE:To limit the number of grain boundary junction in a superconducting circuit by providing an electrode region having high critical current density made of an oxide superconductor thin film, and a tunnel junction made of a crystal grain boundary having low critical current density. CONSTITUTION:A superconducting polycrystal thin film 2 on a polycrystalline substrate 1 is formed of a plurality of crystalline grains 3, and a grain boundary bonds are formed at the grain boundaries 4, 5. In a structure of the junction, only a critical current density of the one junction is suppressed to a lower JL than a value JH of other grain boundary. This equivalent circuit is a series connection of the junctions. In current-voltage characteristics, if a current density is smaller than the JL, a superconducting current flows. If it exceeds the JL, one junction is varied to a voltage state, and continued until it exceeds the JH. When the current is reduced from this state, the current-voltage characteristics become a hysteresis. If the current exceeds the JH, other junction is shifted to the voltage state and the same operation as that of a single Josephson tunnel junction is performed until the current density exceeds the JH.
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