Current understanding of electronic structure and some difficulties with cuprate semiconductors

Experimental observations of the high-T
c
cuprate superconductors are reviewed from the perspective of electronic structures. On the basis of Mott-Hubbard-type band splitting, the semiconductivity, antiferromagnetism, and metallic nature of the cuprate oxides are discussed as a function of the dopant concentration. Then the involvement of the O 2p band which falls between the lower and upper Hubbard bands, as determined by electron spectroscopy, is discussed. Finally, the complex nature of the Fermi surface is considered, and the importance of the involvement of both the O 2p and the lower Hubbard band is stressed.