Normal-state resistivity anisotropy in underdoped RBa2Cu3O6+x crystals

We have revealed new features in the out-of-plane resistivity rho(c) of hea vily underdoped RBa2Cu3O6+x (R = Tm,Lu) single crystals, which give evidenc e for two distinct mechanisms contributing to the c-axis transport. We have observed a crossover towards "metal-like" (partial derivative rho(c)/parti al derivative T > 0) behavior at the temperature T-m which quickly increase s with decreasing doping. The metal-like conductivity contribution dominate s at T < T-m and provides a saturation of the resistivity anisotropy, rho(c )/rho(ab). The antiferromagnetic ordering is found to block this metal-like part of the c-axis conductivity and complete decoupling of CuO2 planes, wh ich may be the reason of superconductivity disappearance.