Two Pseudogap Behavior in La2-xSrxCuO4: Thermoelectric Power at High Temperature

Abstract

Thermoelectric power (TEP) of high-T C superconductors has been investigated in a wide range of temperature (T C < T < 700 K) for La2−x Sr x CuO4. TEP of La2−x Sr x CuO4 shows different temperature dependences in three temperature regions. In the low-temperature region, a positive broad TEP peak is observed near T p, which shifts to lower temperature upon doping. As temperature increases, TEP decreases linearly at intermediate temperature. In the high-temperature region, TEP deviates from the linear temperature dependence at a certain temperature, T h showing a saturation behavior. As the doping concentration increases, the characteristic temperatures, T C, T p, and T h, show systematic changes. In comparison with pseudogap temperature estimated from other experiments, the large pseudogap behavior in TEP at high temperature has been discussed and distinguished from the small pseudogap observed at lower temperature. A possibility of bound pairs formation in the normal state opening the pseudogap at high temperature is discussed briefly. The coexistence of bound pairs and the normal independent carriers for T C < T < Th could be the origin of the intrinsic inhomogeneity.