Doping Dependence of Anisotropic Resistivities in Trilayered   Superconductor Bi2Sr2Ca2Cu3O10+delta (Bi-2223)
  The doping dependence of the themopower, in-plane resistivity rho_ab(T), out-of-plane resistivity rho_c(T), and susceptibility has been systematically measured for high-quality single crystal Bi2Sr2Ca2Cu3O10+delta. We found that the transition temperature Tc and pseudogap formation temperature T_rho_c*, below which rho_c shows a typical upturn, do not change from their optimum values in the "overdoped" region, even though doping actually proceeds. This suggests that, in overdoped region, the bulk $T_c$ is determined by the always underdoped inner plane, which have a large superconducting gap, while the carriers are mostly doped in the outer planes, which have a large phase stiffness. 
Takenori Fujii, Ichiro Terasaki, Takao Watanabe, and Azusa Matsuda