TRANSPORT ANOMALIES OF HIGH-T(C) OXIDES ABOVE ROOM-TEMPERATURE

Transport properties of La2-xSrCuO4, YBa2Cu3O6+x and Bi1.6Pb0.5Sr1.9-y LayCu1.05Oz have been studied over wide temperature regions. Drastic temperature variations of the Hall coefficients R(H) found in the underdoped region of the hole carriers suggest that there exists a crossover-like change of the electronic state above room temperature. Temperature dependence of other transport properties studied at high temperatures is also discussed in relation to this anomalous behavior of R(H). These results elucidate the formation process of the abnormal metallic state of high-T(c) oxides at low temperatures, the existence of which characterizes the metal-insulator transition of the Cu-oxide system as a new-type Mott-Hubbard transition.