The anomalous thermoelectric power of the La doped Bi-2201 phase

Samples of the system with different oxygen contents have been obtained by annealing the as-grown samples at different temperatures and oxygen partial pressures. The results of resistivity and thermoelectric power (TEP) measurements of these samples are reported here. Some anomalous phenomena in transport for the underdoped sample of were observed, i.e., below a characteristic temperature, the TEP exhibits a significant enhancement and the temperature dependence of the resistivity deviates downward from linearity. These results imply that a spin gap exists in the La doped Bi-2201 system. By comparison with the results reported previously, we suggest that the microstructural characteristics are another important factor in determining the spin excitation spectrum.