THE ANOMALOUS THERMOELECTRIC-POWER OF THE LA DOPED BI-2201 PHASE

Samples of the Bi1.9Sr1.6La0.4CuOy system with different oxygen conten ts have been obtained by annealing the as-grown samples at different t emperatures and oxygen partial pressures. The results of resistivity a nd thermoelectric power (TEP) measurements of these samples are report ed here. Some anomalous phenomena in transport for the underdoped samp le of Bi1.9Sr1.6La0.4CuOy were observed, i.e., below a characteristic temperature, the TEP exhibits a significant enhancement and the temper ature dependence of the resistivity deviates downward from linearity. These results imply that a spin gap exists in the La doped Bi-2201 sys tem. By comparison with the results reported previously, we suggest th at the microstructural characteristics are another important factor in determining the spin excitation spectrum.