Zn-doping effect on the normal-state charge transport in untwinned YBa2CU3O7-delta single crystals at low temperatures

The in-plane normal-state resistivity rho (a) of Zn-doped untwinned YBa2Cu3 O7-delta (YBCO) single crystals is measured down to low temperatures by sup pressing superconductivity with magnetic fields up to 18 T. Zn impurities i n the CuO2 planes are found to induce an unusual upturn in rho (a)(T) in "c lean" samples with k(Gamma)l similar or equal to 7. Such an upturn is obser ved only in the samples with oxygen contents of y less than or equal to 6.7 5, which suggests that a metal-insulator crossover takes place at the oxyge n content of y similar to 6.75 in YBCO. (C) 2001 Elsevier Science B.V. All rights reserved.