NORMAL-STATE RESISTIVITY OF SUPERCONDUCTING BI1.95SR1.65LA0.4CUO6+DELTA SINGLE-CRYSTALS

The anisotropy of the normal-state resistivity of a number of superconducting Bi1.95Sr1.65La0.4CuO6+delta single crystals has been measured by using both a six- and a four-terminal technique. We find that the ab-plane resistivity rho(ab) in general increases almost linearly with temperature (d rho(ab)/dT > 0). The temperature variation of the c-axis resistivity rho(c), however, is strongly sample dependent. Both metallic-like (d rho(c)/dT > 0) and mixed temperature dependences of rho(c), including d rho(c)/dT < 0 are observed. The mixed rho(c)(T) data can be well described by fitting to rho(c)(T) = A + BT + C/T, indicating that the temperature dependence of rho(c)(T) is the result of a competition between metallic and non-metallic terms. The temperature T-min at which rho(c) reaches a minimum increases with increasing d rho(ab)/dT, suggesting that the metallic term of rho(c) arises from misaligned Cu-O planes. This is confirmed by an electron-microscope (HRTEM) analysis of the samples. The anisotropy ratio rho(c)/rho(ab) is of the order of 10(3) but increases monotonically with decreasing temperature, indicating differences in the scattering processes parallel and perpendicular to the Cu-O plane.