Josephson junction device formed of oxide superconductor and process for preparing the same

A Josephson junction device, comprising:

• a single crystalline substrate including a principal surface,
• a layer of the same material as the substrate formed on the principal surface of the substrate so as to form a step on the principal surface, and
• an oxide superconductor thin film formed on the principal surface of the substrate, said oxide superconductor thin film including:
• first and second superconducting portions respectively positioned above and below the step and constituted of single crystals of the oxide superconductor,
• a junction portion between the first and second superconducting portions, said junction portion being constituted of a single crystal of the oxide superconductor having a crystal orientation which is different from those of the first and second superconducting portions, and
• grain boundaries between the first superconducting portion and the junction portion and between the second superconducting portion and the junction portion constituting a weak link of the Josephson junction,
• wherein the first and second portions of the oxide superconductor thin film have their c-axes perpendicular to the principal surface of the substrate and the junction portion has its c-axes parallel to the principal surface of the substrate, and wherein an edge of said step is substantially perpendicular to the principal surface of the substrate.