COEXISTENCE OF BOUND PAIRS AND INDEPENDENT CARRIERS IN THE NORMAL-STATE OF HIGH T-C SUPERCONDUCTORS - THERMOELECTRIC-POWER

Unlike the low T-c superconductors, the high T-c superconductors have various anomalous features in their normal states. Among them, thermoe lectric power(TEP) shows one of the most unusual properties. The magni tude of TEP is very small characteristic to that of the broad band met als, whereas the temperature dependence of TEP is semiconductor-like, i.e., it increases upon cooling. To understand such an anomalous featu re, we have proposed a phenomenological mixed state of bound pairs and independent carriers in normal state. The bound pairs are assumed not to be correlated with each other at T>T-c and the number of bound pai rs decreases as temperature increases. With this model, one can calcul ate that the configuration entropy increases upon cooling (assuming th e density of state is constant as a function of temperature) and hence the anomalous TEP data can be fitted. The strongly correlated nature of cuprate superconductors can justify the existence of such bound pai rs in normal state. However, the physical origin of the bound pairs is not understood. Results are compared with the pseudo gap observations in normal state of cuprate superconductors.