THERMOPOWER AND RESISTIVITY OF LA-DOPED THALLIUM-1201 AND BISMUTH-2201 SUPERCONDUCTORS

We have measured the thermopower and resistivity of two series of cupr ate superconductor, Tl(0.5)Pb(0.5)Sr(2-x)La(x)Cu0(5) and Bi2Sr2-xLaxCu O6+y, which possess a single CuO2, plane. In each series, the hole con centration can be varied by changing the La content, permitting invest igation of the overdoped, maximum-T-c and underdoped regimes. The ther mopower follows a pattern similar to that seen in superconductor serie s with more than one CuO, plane, namely an approximately linear decrea se as temperature increases well above T-c. However, the thermopower s hows a minimum above T-c followed by a maximum as temperature increase s for samples with a small thermopower and high T-c. The magnitude of thermopower as a function of T-c is in general agreement with the univ ersal behaviour found for other cuprate superconductors.