C-axis resistivity of Bi 2Sr 2CaCu 2O y thin films at various oxygen doping: Phase diagram and scaling law

Abstract

We compare the temperature-dependence of the in-plane and c-axis resistivity, ρ ab ( T) and ρ c ( T), of Bi 2Sr 2CaCu 2O y . 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. ρ c ( T) exhibits a metallic behaviour at high T followed by a semiconducting-like behaviour at lower T, interrupted by the superconducting transition: ρ c ( T) is minimum at T min and maximum at T P, T min is defined as the temperature where the pseudogap opens. T min, 1.4 larger than the temperature T ∗, below which the pseudogap signature is seen in ρ ab ( T), exhibits the same dependence on hole doping p. A phase diagram ( T, p) is established with these characteristic temperatures. Interestingly ρ c ( T) normalized by its value at T min obeys a scaling law vs T/ T min. This confirms that T min is the important energy scale in the normal state c-axis transport.