Thermopower and resistivity of La-doped thallium 1201 and bismuth 2204 superconductors

Abstract

We have measured the thermopower and resistivity of two series of cuprate superconductor, Tl0.5Pb0.5Sr2-xLaxCuO5 and Bi2Sr2-xLaxCuO6+y, which possess a single CuO2 plane. In each series, the hole concentration can be varied by changing the La content, permitting investigation of the overdoped, maximum-Tc and underdoped regimes. The thermopower follows a pattern similar to that seen in superconductor series with more than one CuO2 plane, namely an approximately linear decrease as temperature increases well above Tc. However, the thermopower shows a minimum above Tc followed by a maximum as temperature increases for samples with a small thermopower and high Tc. The magnitude of thermopower as a function of Tc is in general agreement with the universal behaviour found for other cuprate superconductors.