Thermoelectric power of La_2-xSr_xCuO₄ at high temperatures

Thermoelectric power (TEP) of high-T_c superconductors has been investigated in a wide range of temperature (T_c < T < 700 K) for La_2-xSr_xCuO₄. For wide doping level from underdoping to heavily overdoping, TEP follows the linear-T dependence above the broad peak temperature, T_p. At high temperatures, however, TEP shows deviation from the linear-T dependence at a certain temperature T_h, which is pronounced with doping up to x ∼ 0.2 and turns to be suppressed for further doping. The systematic change of the characteristic temperatures, T_c, T_p, and T_h discussed in terms of the crossover behavior from a pseudogap state to strange metal in the underdoped regime and from strange metal to conventional metal in the overdoped regime.