Variation of Tc 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 normal state of the Bi2Sr2CaCu2O8 system over a wide range of carrier concentration. The carrier concentration is varied by partial replacement of Ca by Y ions. The superconducting transition temperature (T-c,) is found to decrease considerably and a significant enhancement of the thermopower is observed with increasing Co doping. Both T-c and thermopower show linear dependence on Co concentration. The temperature dependence of the thermopower for the underdoped samples shows a weak anomaly above the broad peak. This anomaly may be assigned to the opening of a normal-state gap in the density of states. A scaling behavior for the normal-state thermopower for optimum and underdoped samples has been established from our studies. We have also shown that the thermopower of all underdoped cuprates can be scaled into a single universal functional form. [S0163-1829(99)09325-X].