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A high-resolution spatially resolved study of electrical inhomogeneties in high-Tc thin films by Laser Scanning Microscopy has been carried out. A laser beam was focused onto a submicrometer spot on the surface of the thin film microbridge resulting in an increase in its local temperature. Bolometric or thermo-electric effects in the heated region result in a voltage change across the sample that has been measured as a function of the beam position. These two electrical images have been compared with optical images formed by subtracting two conventional images taken with polarized light. The correlation between the three images strongly suggest that interfaces between grains with different twin boundary orientations are more resistive than interfaces between grains with the same twin boundary orientation.

Single crystals of YBa2Cu3O7-δ (YBCO) have been detwinned under the simultaneous application of heat and uniaxial stress. This approach, however, has proved futile in thin films as they become heavily twinned due to strain from the underlying substrate as well as the orthorhombic unit cell. This lack of control over twinning has made it difficult to determine the role that twins play in determining the transport properties of films. Here, we present a technique for detwinning YBCO thin films. The detwinning in YBCO thin film is achieved by suspending a portion of the YBCO film above the underlying substrate. The suspended material is no longer influenced by the confining effects of the substrate and this allows it to detwin under the application of a uniaxial stress brought about by an anneal. With this technique, we are able to produce high-quality detwinned regions that will help aid the understanding of transport mechanisms in YBCO.

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