Abstract
Inhomogeneity is one of the most important problems for the investigation of the superconductor-insulator transition. Y and Pb co-doped Bi2Sr2CaCu2O8+δ(PbY-Bi2212) crystals were fabricated by the self-flax method in order to control both carrier density and dimensionality. The Y-content of PbY-Bi2212 crystals was much wide distributed in the same crucible rather than that of only Y doping Bi2212 (Y-Bi2212) crystals. In order to clear the origin of inhomogeneity, crystals were characterized by wavelength-dispersive X-ray spectroscopy (WDS) and X-ray diffraction (XRD). One can estimate the Y-content of cleavage samples from the c-axis lattice parameter obtained by XRD because mainly Y-con- tent affects to c-axis lattice constant for both Y-Bi2212 and PbY-Bi2212 crystals. It found that there are some samples with multi-phases and the ratio of samples with multi-phase for PbY-Bi2212 crystals is larger than that for Y-Bi2212 crystals. The linear relation between Y-content and Pb-content were also found from WDS. Large inhomogeneity of Y-content may be induced from Pb-content inhomogeneity. Transport properties are strongly dependent to Y-content. However they cannot be explained only from the macroscopic chemical compositions of the substitution atom Y and Pb. It may be related to microscopic inhomogeneity.
Highlights
The superconductor-insulator transition (SIT) has been intensively studied in homogeneously disordered twodimensional (2D) thin films since the late 1980s [1,2,3]
In order to clear the origin of inhomogeneity, crystals were characterized by wavelength-dispersive X-ray spectroscopy (WDS) and X-ray diffraction (XRD)
While we have reported the inhomogeneity of the Y-content for Y-Bi2212 crystals [8], Y-content is much wide distribute for PbY-Bi2212 crystal rather than for Y-Bi2212 ones
Summary
The superconductor-insulator transition (SIT) has been intensively studied in homogeneously disordered twodimensional (2D) thin films since the late 1980s [1,2,3]. High-Tc cuprate superconductors (HTSC) are quasi-2D system, and the SIT of them has been reported on many kinds of samples [3]. These reports indicate the existence of a threshold sheet resistance. We have so far investigated the SIT for HTSC thin films and single crystals [6,7,8]. Bi2Sr2CaCu2O8+y (Bi2212) is one of the highest anisotropy systems among HTSCs. the doping control SIT for Bi2212 single crystals is selected as our research target. Inhomogeneity is one of the most important problems for studying the doping controlled SIT. In this report the effect of Pb substitution on the inhomogeneity and transport property is studied in order to analyze atomic compositions and to measures transport properties
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