LOW-TEMPERATURE RESISTIVITY OF YBA2CU3O6-CRYSTALS IN THE NORMAL-STATE(X SINGLE)

A scan of the superconductor-nonsuperconductor transformation in singl e crystals of YBa2Cu3O6+x (x approximate to 0.37) is done in two alter native ways, namely, by applying a magnetic field and by reducing the hole concentration through oxygen rearrangement. The in-plane normal-s tate resistivity rho(ab) Obtained in the two cases is quite similar; i ts temperature dependence can be fitted by a logarithmic law in a temp erature range of almost two decades. However, an alternative represent ation of the temperature dependence of sigma(ab) = 1/rho(ab) by a powe r law, typical for a 3D material near a metal-insulator transition, is also plausible. The vertical conductivity sigma(c) = 1/p(c) followed a power law, and neither sigma(c)(T), nor rho(c)(T) could be fitted by log T. It follows from the rho(c) measurements that the transformatio n at T = 0 is split into two transitions: superconductor- normal-metal and normal-metal-insulator. In our samples, they are separated in oxy gen content by Delta x approximate to 0.025. (C) 1997 American Institu te of Physics.