THERMOPOWER OF BI2-XPBXSR2CACU2O8+DELTA

We report resistivity and thermopower measurements on a series of Pb-substituted ceramic samples of Bi2Sr2CaCu2O8+delta. The samples show an increase in their conductivity and a systematic fall to more negative values of thermopower as holes are added with the introduction of progressively more Pb or oxygen, trends held in common with other high-T(c) superconductors. Furthermore, the thermopower falls linearly with increasing temperature in all of our samples, with the unusual property that it extrapolates to a large (typically > 5-mu-V/K) nonzero value at zero temperature. This offset value decreases dramatically as holes are added, whereas the linear slope shows a much weaker decrease. This temperature dependence can be fitted to a model in which the thermopower is strongly enhanced at low temperatures by the electron-phonon interaction.