Thermopower of high-Tc cuprates

We have studied the thermopower of La2CuO4+z and Nd2CuO4-y which undergo an antiferromagnetic transition near room temperature and Bi2Sr2-xLaxCuO6+tau for which a broad spectrum of doping is possible. The thermopower of La2CuO4+z and Nd2CuO4-y is seen to exhibit an anomaly at the Neel temperature, whereas the resistivity is not. The extrapolated zero-temperature intercept of the thermopower, which is known to be positive for hole-doped cuprate superconductors, is found to become negative for Bi2Sr2-xLaxCuO6+z above some critical doping level. The data strongly suggest that the thermopower of high-T-c cuprates contains a large amount of extra contribution in addition to the usual diffusion thermopower. We discuss origins of the extra contribution in the thermopower. [S0163-5824(99)03701-7].