Transport measurements in overdoped YBCO thin films

Temperature dependence of Hall constant R_H and longitudinal resistivity ρ_xx have been measured in Ca-doped YBCO thin films with varying oxygen contents, with emphasis on the overdoped regime. R_H vs. T data present a peak near T_c whose height reduces with doping and disappears at optimal doping. Unexpectedly, the peak reappears above optimal doping with a height that increases with doping. A similar behavior was observed in the parameters that fit cot(θ_H) vs. T to a parabola. They decrease smoothly with increasing doping in the underdoped region and present a peculiar peak in the overdoped region. This behavior might indicate the crossover to a new regime of transport properties in strongly overdoped HTSC. We discuss the possible origin and implications of these results.