Variation of T-c and transport properties of the Co-doped Bi2Sr2Ca1-xYxCu2O8 system

We report the effect of the substitution of the 3d transition metal element Co for Cu on the resistivity, Hall coefficient, and thermopower in the nor mal state of the Bi2Sr2CaCu2O8 system over a wide range of carrier concentr ation. The carrier concentration is varied by partial replacement of Ca by Y ions. The superconducting transition temperature (T-c,) is found to decre ase considerably and a significant enhancement of the thermopower is observ ed with increasing Co doping. Both T-c and thermopower show linear dependen ce on Co concentration. The temperature dependence of the thermopower for t he underdoped samples shows a weak anomaly above the broad peak. This anoma ly may be assigned to the opening of a normal-state gap in the density of s tates. A scaling behavior for the normal-state thermopower for optimum and underdoped samples has been established from our studies. We have also show n that the thermopower of all underdoped cuprates can be scaled into a sing le universal functional form. [S0163-1829(99)09325-X].