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It is possible to map the linear defect structure of a YBa2Cu3O7-delta superconducting thin film quantitatively. There is a connection between the as-grown dislocation density and the strong pinning behaviour of the superconducting current density in these films. There is clear evidence that the high current densities in YBa2Cu3O7-delta thin films are caused by strong vortex pinning by natural linear defects. This indicates that it could be possible to investigate vortex matter in films with a tailored non-random distribution of linear strong pinning defects.

A mechanical procedure that involves generation of a weak perturbation in substrate surface using a diamond needle prior to film deposition yields Josephson junctions with high Tc and SQUIDS. Modification of film thickness controls function parameters whose magnitude can be varied by many orders. Critical junction current densities range from 5 x 10 to the 4th power to 1 x 10 to the 5th power A per squared cm at 77 K. The junctions exhibit Shapiro steps on exposure to rf power. The current-voltage properties do not exhibit hysteresis and are resistively shunted. An optimum peak voltage response to dc flux of 12 microvolts at 77 K is seen in dc SQUIDS.

Very thin films (less than 20 nm) of La[sub 0.73]Ca[sub 0.27]MnO[sub 3] on SrTiO[sub 3] substrates exhibit properties quite different from the bulk; they are ferromagnetic insulators instead of ferromagnetic metals. Electron microscopy shows that such thin films are perfectly smooth, single phase and crystalline, as are thicker films but that they have a structure (imposed by the lattice matching with the substrate) which is different from that of the bulk or thick films (much greater than 20 nm). The main features of this structure are a Jahn-Teller distortion of the MnO[sub 6] octahedra (not present in the bulk) and tilts of the MnO[sub 6] octahedra (different from the bulk). [ABSTRACT FROM AUTHOR]