Electric field induced resistance switching has been investigated for perovskite-oxide heterojunctions consisting of various metal electrodes and p-type or n-type semiconducting perovskite oxides such as Pr0.7Ca0.3MnO3 or Nb-doped SrTiO3, respectively. The metal/perovskite-oxide heterojunction devices show either ohmic or rectifying I-V characteristics similar to those of a Schottky junction, depending on the work function of the metals. In addition, the rectifying I-V characteristics have large hysteresis. Corresponding to the hysteresis directions, the junction devices show reversible resistance switching upon voltage pulse applications. On the basis of the experimental results, we propose that the resistance switching and memory effect are originated by a charging effect in the trapping states at the Schottky-like metal/perovskite-oxide interfaces.
We investigated the current-voltage characteristics and critical scaling behavior in c-axis oriented YBa2Cu3O7-(delta ) (YBCO) films whose thicknesses are from 18 nm to 230 nm, in magnetic fields applied perpendicular to the film surface. The vortex-glass transition temperature (Tg) decreased as the thickness decreased, and wide temperature critical scaling region was observed in thinner films. We note that the reduction of Tg is similar to the reported result of the vortex-glass transition of narrow YBCO strip lines, and that wide temperature critical scaling region was also observed in the vortex-glass transition of Bi2Sr2Ca2Cu3Ox (Bi-2223) films. From the analogy to the study of Bi-2223 films, we suggest that, in the thinner YBCO films, the vortex-glass correlation length parallel to the c-axis (xi) g// is limited by the film thickness, and that wide critical scaling region originates from the enhanced thermal fluctuation effect brought by the reduced correlation volume through the interruption of vortex correlation along c-axis.
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