Relation between inhomogeneous structure and transport properties for superconductor-insulator transitions

Le résumé fourni par la source

In the study of superconductor-insulator transitions of high- T c cuprates complicated behaviors in transport properties were observed for example quasi-reentrant behaviors. In this study we report that the relation between microscopic structure and transport properties for Bi 2 Sr 2 CaCu 2 O 8+y crystal with substitution of Ca by Y. From the energy dispersive X-ray spectroscopy it was estimated that samples contain almost 45% Y when the starting composition was only 10% Y. Also the values of c-axis length were almost constant and shorter than those of Y free samples. However there were various ρ (T) behaviors dependent on sample: localized, quasi-reentrant, broad superconducting transition etc. All sheet resistances defined per CuO 2 bilayer in the normal state were much larger than the quantum resistance h /4e 2 or 6450 Ω. We were able to observe the inhomogeneous distribution of Y using a combination of electron energy loss spectroscopy and a high-angle annular dark-field technique in a scanning transmission electron microscope. The Y rich region formed the belt with about 20 nm width. This inhomogeneous structure seems to be the origin of various transport properties.

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