Effect of Nickel Impurities on Superconductivity and Electrical Resistivity of the High- T c Superconductor Ba 2 YCu 3 O 7

Abstract

The influence of substituting Ni for Cu on the superconducting critical temperature T_c and the electrical resistivity ρ(T) of the high-T_c superconductor Ba₂YCu₃O₇ is reported. In the series Ba₂YCu_3(1-x)Ni_3xO₇ we find up to x = 0.12 a linear depression of T_c with a slope of (dT_c/dx)_x=0 = -2.4 K/(% substituted Cu). A set of samples with nominal composition Ba₂YCu_3(1-x)O_7+δ prepared for comparison shows in the same x-range no change in T_c. In both series the resistance ratios R(300 K)/R(125 K) decrease to about 1 for x = 0.12, however, only the samples containing large amounts of Ni exhibit a pronounced positive curvature of ρ(T). The results are discussed in the framework of Abrikosov-Gorkov theory, i.e. the pairbreaking effect of the exchange interaction of the conduction electrons with the magnetic moments of the Ni-impurities.