Electronic properties of hole- and electron-dopedT’-,T*-, and infinite-layer-type high-Tccuprates

We compare the electronic structure of n-type and p-type dopable high-${\mathit{T}}_{\mathit{c}}$ cuprates, namely the hole-doped ${\mathrm{Nd}}_{1.4}$ ${\mathrm{Ce}}_{0.2}$ ${\mathrm{Sr}}_{0.4}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{\delta }}$ (${\mathit{T}}^{\mathrm{*}}$) system as well as the electron-doped ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{\delta }}$ (T’) and ${\mathrm{Sr}}_{0.85}$ ${\mathrm{Nd}}_{0.15}$ ${\mathrm{CuO}}_{2\mathrm{-}\mathrm{\delta }}$ (‘‘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-${\mathit{T}}_{\mathit{c}}$ cuprates is a comparatively high value of the Cu 3d Coulomb interaction ${\mathit{U}}_{\mathit{d}\mathit{d}}$. This is concluded from model calculations on core-level and valence-band spectra. Also the superconducting infinite-layer compound ${\mathrm{Sr}}_{0.85}$ ${\mathrm{Nd}}_{0.15}$ ${\mathrm{CuO}}_{2\mathrm{-}\mathrm{\delta }}$ exhibits (besides a remarkably low Cu-O hybridization) this enhanced value of ${\mathit{U}}_{\mathit{d}\mathit{d}}$. For the rare-earth layers of T’ and ${\mathit{T}}^{\mathrm{*}}$ we find small but characteristic differences in the electronic properties (Nd-O-hybridization and charge-transfer energy), which can be attributed to structural differences.