Growth and superconductivity of Bi 2Sr 2Ca 1− xY xCu 2O 8+δ single crystals in the Tc optimum region

Abstract

Bi 2Sr 2Ca 1− x Y x Cu 2O 8+δ single crystals with low Y concentrations were grown by a self-flux method and characterized structurally by electron microscopy. Furthermore, their superconducting properties were investigated by magnetic measurements. By substituting Y 3+ for Ca 2+ in Bi 2Sr 2CaCu 2O 8+δ (Bi-2212) the doping level is varied from the overdoped ( T c = 82 K) to the underdoped ( T c = 87 K) rgion with an optimum level that corresponds to a high T c (onset) value of 91.5 K. Moreover, this optimal composition yields higher irreversibility line and J c values than any other as-grown Bi-2212 crystal. The superconducting parameters of the crystals were deduced from reversible magnetization measurements. The λ ab (0) values are found to increase when x increases, i.e. as the doping level decreases. 2D scaling of the fluctuations for different doping levels shows that the strength of the fluctuations, obtained from the Ginzburg parameter G i , increases as the Y concentration increases, i.e. as the doping level decreases.