Implications of crystal-field and intra-atomic interactions for the electronic structure of high-T_{c} superconductors

Abstract

The energies of Cu 3d and O 2p ion orbitals in the ion-lattice potentials of ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ and ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$, and the intra-atomic energies of various ${\mathrm{Cu}}^{3+}$(3d${)}^8$ configurations, are calculated. The results suggest that electrons removed from the ${\mathrm{CuO}}_2$ layer to accomodate doping in ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ or the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ stoichiometry come not from &’s and their O 2pσ bonding partners but from otherwise filled π-bonding orbitals. The resulting two types of bonds and/or bands may be important for superconductivity.