Anomalous Thermoelectric Power of the High-Tc Materials in Normal State: Both Copper Oxides and C60 Fullerene

Abstract

We have measured the temperature dependence of thermoelectric power (TEP) and resistivity for the cuprate superconductors and the alkali metal doped bulk C60 fullerenes. The results for both high T c materials are anomalous. The magnitude of TEP is small characteristic to that of the broad band metal. But the temperature dependent TEP of cuprate superconductors are semiconductor-like. To understand this somewhat controversial behavior, we propose the so called ‘mixed state model’ where the independent bound pairs and single-particle-like carriers coexist in the normal state, T > T c , This mixed state model is compared with the local pair theory, as well as the marginal Fermi liquid theory. For the alkali metal doped bulk C60 fullerenes, the TEP shows two types of temperature dependences. One is very much anomalous with positive TEP values and the other is less anomalous in a sense that it is more or less simple metallic with negative TEP values. In both types, however, there exist electronic transitions in 70K < T < 200K.