Spatially resolved analysis of high-T c grain boundary Josephson junctions and arrays

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Abstract
Using Low Temperature Scanning Electron Microscopy (LTSEM) we have studied the spread of the critical current values in one‐ and two‐dimensional arrays of high‐Tc grain boundary Josephson junctions (GBJs). For series arrays the critical current values and the magnetic field dependences of all GBJs within the array could be imaged by LTSEM. Our measurements showed that part of the spread of the critical current values derived from measurements of the current‐voltage characteristics is caused by variations of the local magnetic field at the junction position. For bicrystal GBJs a Gaussian distribution of the critical current values with a spread as small as ±20% was found. For the investigated step‐edge and biepitaxial GBJs the spread of the critical current values was considerably larger. The LTSEM technique also was used to study the spatial homogeneity of the critical current density of the different types of YBa2Cu3O7−δ grain boundary Josephson junctions with a spatial resolution of 1μm. Whereas the critical current density of bicrystal GBJs showed only small variations on this length scale, strong inhomogeneities were found for step‐edge and biepitaxial GBJs.