John B. Goodenough

Improved J/sub c/ of bilayer YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film structures

Critical-current (J/sub c/) measurements for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO), Gd/sub 0.6/Ca/sub 0.4/Ba/sub 1.6/La/sub 0.4/Cu/sub 3/O/sub 7-/spl delta// (TX-GBCO) and TX-GBCO/YBCO bilayers were performed with transport measurements at different applied magnetic fields. The film samples were prepared by pulsed laser deposition and patterned as microbridges. The highest J/sub c/ (1.5/spl times/10/sup 6/ A/cm/sup 2/) at 75 K in 5 Tesla (Hllab) was observed for TX-GBCO/YBCO bilayers, which showed a 40% increase in J/sub c/ over YBCO under the same conditions. The bilayer samples possess a T/sub c/ at 90 K and display superconducting properties similar to YBCO. A possible mechanisms for the high J/sub c/ of bilayer YBCO films is discussed. Development of these bilayer and multilayer structures represents a promising new direction to improve the superconducting properties of YBCO since the TX-GBCO layer provide both protection against corrosion and a significant improvement in J/sub c/.Critical-current (J c ) measurements for YBa 2 Cu 3 O 7-δ (YBCO), Gd 0.6 Ca 0.4 Ba 1.6 La 0.4 Cu 3 O 7-δ (TX-GBCO) and TX-GBCO/YBCO bilayers were performed with transport measurements at different applied magnetic fields. The film samples were prepared by pulsed laser deposition n and patterned as microbridges. The highest J c (1. 5 X 10 6 A/cm 2 ) at 75 K in 5 Tesla (Hllab) was observed for TX-GBCO/YBCO bilayers, which showed a 40 % increase in J c over YBCO under the same conditions. The bilayer samples possess a T c at 90 K and display superconducting properties similar to YBCO. A possible mechanisms for the high J c of bilayer YBCO films is discussed. Development of these bilayer and multilayer structures represents a promising new direction to improve the superconducting properties of YBCO since the TX-GBCO layer provide both protection against corrosion and a significant improvement in J c .

Development of ramp-edge SNS junctions using highly stable normal-metal barrier materials

By using a cation-modified and corrosion-resistant compound of (Pr/sub y/Gd/sub 0.6-y/)Ca/sub 0.4/Ba/sub 1.6/La/sub 0.4/Cu/sub 3/O/sub 7/ (y=0.4, 0.5, and 0.6) as normal-metal barrier materials, high-temperature superconducting Josephson junctions have been fabricated in a ramp-edge superconductor/normal-metal/superconductor (SNS) configuration. We have tuned the Pr substitution level in order to achieve the optimal electrical resistivity of the barrier layer for high-performance SNS junctions. The junctions fabricated with these normal-metal barriers show well-defined RSJ-like current vs voltage characteristics at liquid-nitrogen temperature. The junction performance is mainly controlled by the N-layer instead of the interface. We have also fabricated dc superconducting quantum interference devices based on ramp-edge SNS technology with these normal-metal barriers. The ratio of peak-to-peak voltage modulation of the superconducting quantum interference devices to the I/sub c/R/sub n/ product is more than 30%.