ELECTRONIC-PROPERTIES OF HOLE-DOPED AND ELECTRON-DOPED T'-LAYER-TYPE, T-ASTERISK-LAYER-TYPE, AND INFINITE-LAYER-TYPE HIGH-TC CUPRATES

We compare the electronic structure of n-type and p-type dopable high-T(c) cuprates, namely the hole-doped Nd1.4Ce0.2Sr0.4CuO4-delta (T*) system as well as the electron-doped Nd2-CexCuO4-delta (T') and Sr0.85Nd0.15CuO2-delta (''infinite-layer'') systems. Investigations were done mainly by means of core-level and valence-band photoemission spectroscopy. Also we performed auxiliary measurements of Hall effect and magnetic susceptibility. From the investigations on the Cu-O layers we propose that one criterion for electron dopability in high-T(c) cuprates is a comparatively high value of the Cu 3d Coulomb interaction U(dd). This is concluded from model calculations on core-level and valence-band spectra. Also the superconducting infinite-layer compound Sr0.85Nd0.15CuO2-delta exhibits (besides a remarkably low Cu-O hybridization) this enhanced value of U(dd). For the rare-earth layers of T' and T* we find small but characteristic differences in the electronic properties (Nd-0-hybridization and charge-transfer energy), which can be attributed to structural differences. Crystal-field splitting of Nd 4f levels and antiferromagnetic coupling of Nd3+ moments in Nd1.85Ce0.15CuO4-delta and Nd1.4Ce0.2Sr0.4CuO4-delta have been investigated by evaluation of the magnetic susceptibility. The dopant ions cerium for T' and T* and neodymium for Sr0.85Nd0.15CuO2-delta are found to be tetra- and trivalent, respectively, which confirms again that the infinite-layer compound is an electron-doped cuprate.