Origin of nonuniform properties of YBa2Cu3 O7−x/CaRuO3/YBa2Cu3O7−x Josephson edge junctions

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Abstract
The fine scale microstructure of YBa2Cu3O7−x (YBCO)/CaRuO3 (CRO)/YBCO edge junctions has been characterized using transmission electron microscopy. The results showed that the damages due to ion beam milling during fabrication of the YBCO edges annealed out during heating to higher temperatures for deposition of additional layers. No contamination due to the ex situ processing of the edges was detected. The CRO grew epitaxially on the YBCO edge and small insulating Y2O3 particles nucleated on the CRO giving rise to inhomogeneous electrical properties along the junction. The nucleation of Y2O3 particles was enhanced by the microscopically rough morphology of the YBCO edge. The results stress the importance of the morphology of the YBCO edge and show that general conclusions about the interface structure cannot be drawn from corresponding planar geometries.