Scaling of the Hall coefficient and resistivity in underdoped and overdoped RBa2Cu3Oy films.

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We have studied the normal-state transport properties, the resistivity ρ(T), and the Hall coefficient RH(T) on two sets of samples of RBa2Cu3Oy compounds (R=Y,Sm) away from optimal doping. In the overdoped regime, RH(T) obtained from Ca-doped SmBa2Cu3Oy shows a saturation at high temperature. While RH(T) decreases with T at low temperature, it becomes temperature independent when the temperature exceeds a certain value T*H. This characteristic T*H decreases with doping, and is only visible in our experimental temperature range when the samples are sufficiently doped. By assuming a universal functional form for all doping levels, the temperature dependence of the Hall coefficient can be scaled. Another characteristic temperature T*ρ can be seen from the resistivity data in the underdoped regime, obtained from the oxygen-deficient YBa2Cu3Oy samples. Above T*ρ, ρ(T) increases almost linearly with T, whereas below, it deviates from the linear behavior. We discuss the relationship between these two characteristic temperatures T*H and T*ρ for different doping levels. For the underdoped samples, the resistivity is fitted well by the relation ρ(T)≊aRH(T)T2+b.