Thermopower of Bi₂Sr₂Ca_1-xR_xCu₂O_y (R = Gd, Pr) single crystals

The temperature and carrier concentration dependence of the thermopower (TEP) S in Bi₂Sr₂Ca_1-xR_xCu₂O_y (R = Gd, Pr) single crystals were carefully studied. Upon Gd or Pr doping, the superconductivity changes systematically from overdoping to underdoping with the TEP increasing monotonically. S(T)/S(T_scale) against T/T_scale for all the underdoped crystals can be well scaled into a universal curve, where T_scale is the temperature at which S begins to deviate from T-linear behaviour. This scaling behaviour is assumed to correlate with the opening of the pseudogap. Furthermore, the temperature dependence of the TEP is analysed and discussed in terms of two different two-band models and the Nagaosa-Lee model.