c-axis resistivity of Bi2Sr2CaCu2Oy thin films at various oxygen doping: Phase diagram and scaling law

We compare the temperature-dependence of the in-plane and c-axis resistivity, ρab(T) and ρc(T), of Bi2Sr2CaCu2Oy. Measurements have been made on a thin film deposited on a vicinal substrate, examined in various doping states by removing oxygen in steps from the overdoped to very underdoped states. ρc(T) exhibits a metallic behaviour at high T followed by a semiconducting-like behaviour at lower T, interrupted by the superconducting transition: ρc(T) is minimum at Tmin and maximum at TP, Tmin is defined as the temperature where the pseudogap opens. Tmin, 1.4 larger than the temperature T*, below which the pseudogap signature is seen in ρab(T), exhibits the same dependence on hole doping p. A phase diagram (T, p) is established with these characteristic temperatures. Interestingly ρc(T) normalized by its value at Tmin obeys a scaling law vs T/Tmin. This confirms that Tmin is the important energy scale in the normal state c-axis transport