NONMONOTONIC EVOLUTION OF OUT-OF-PLANE RESISTIVITY WITH PR DOPING IN Y1-XPRXBA2CU3O7-DELTA SINGLE-CRYSTALS

In-plane (rho(ab)) and out-of-plane (rho(c)) resistivities of Y1-xPrxB a2Cu3O7-delta have been determined using the electrical contact config uration of the de flux transformer. rho(c)(x) varies nonmonotonically with x: rho(c)(x) increases at low x, reaches a maximum at x approxima te to 0.42, and then decreases for higher values of x. In contrast, rh o(ab)(x) increases monotonically with x. These results, along with the coexistence of metallic rho(ab) and semiconducting rho(c), are consis tent with the presence of a gap in the energy spectrum of the CuO chai ns, leading to tunneling through both valence and conduction bands of the CuO chains.