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A planar-type junction of HoBa2Cu3O7−x−La1.5Ba1.5Cu3O7−y −HoBa2Cu3O7−x having an electrode spacing as small as 0.1 μm is fabricated and its electrical characteristics are measured. Supercurrent through the La1.5Ba1.5Cu3O7−y layer is detected up to the temperature of 69 K. A superconducting region extends from the YBa2Cu3O7−x electrodes into a normal La1.5Ba1.5Cu3O7−y layer with a submicrometer scale. The superconducting decay length is 65 nm, which is two orders of magnitude larger than the value calculated from the conventional proximity theory.

A HoBa2Cu3O7-x -La1.5Ba1.5Cu3O7-y -HoBa2Cu3O7-x junction having a planar structure is fabricated and its electrical characteristics are investigated. The planar junction is formed by sectioning a HoBa2Cu3O7-x layer into two superconducting electrodes keeping a submicrometer between them. Supercurrent is detected for the junction with an electrode spacing smaller than 0.4 µm. Critical current is exponentially dependent on electrode spacing. Superconducting decay length for the La1.5Ba1.5Cu3O7-y layer is 65 nm and is almost independent of temperature up to 70 K. This extraordinary long decay length and anomalous superconducting characteristics are not shown to be explained by the conventional proximity theory, and phenomenologically outlined.

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The transport characteristics of Y y Pr 1Ϫy Ba 2 Cu 3 O 7Ϫx thin film systems were systematically investigated as a function of the Y concentration and film thickness. The films in the superconducting state changed their transport characteristics to those of the nonsuperconducting state when the film thickness was decreased beyond the value at which the film sheet resistance is equal to the quantized sheet resistance h/4e 2 . This phenomenon is a kind of superconductor-insulator transition. The resistance-temperature characteristics in the insulator phase are a result of the variable-range-hopping conduction between localized states. The electric-field effect was measured especially in the insulator phase. The resistance modulation ratio ⌬R/R in the insulator phase was much greater than the carrier density modulation ratio ⌬N/N. The ratio of ⌬R/R to ⌬N/N increased as the Y concentration increased. In particular, the (⌬R/R)/(⌬N/N) value reached as high as 50 for a Y 0.9 Pr 0.1 Ba 2 Cu 3 O 7Ϫx film in the insulator phase. Higher (⌬R/R)/ (⌬N/N) values effectively enhance the performance of superconducting field effect transistors.