SPIN GAP EFFECT ON ANISOTROPIC RESISTIVITIES MEASURED ON UNTWINNED YBA2CU3O7-Y

We have investigated the anisotropic resistivities of YBa2Cu3O7-y usin g detwinned crystals with various oxygen contents (6.68 less than or e qual to 7 - y less than or equal to 6.93). Our results show that the m etallic-to-semiconducting crossover in rho(c) is linked with the onset of nonlinearity in rho(a), which seems to be associated with the ''sp in gap''. In addition, we also have studied the Zn-doping effects on t he charge transport and find that the Zn-doping does not affect the co nduction mechanism essentially though it suppresses T-c.