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

Abstract

In the study of superconductor-insulator transitions of high-Tc 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 Bi2Sr2CaCu2O8+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 CuO2 bilayer in the normal state were much larger than the quantum resistance h/4e2 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.