Abstract
The qualitative and quantitative features of the electronic charge distribution in cuprate superconductors are reexamined on the basis of a comprehensive set of nuclear quadrupole resonance and NMR measurements. A systematic analysis of measured electric-field gradients is performed within the tight-binding approach, commonly used for electronic models in cuprates. Both in-plane and out-of-plane sites and orbitals are considered. Special attention is given to the generic model involving only the orbitals in the planes. This model is checked against the experimental data. The physical origin of several material-dependent features is clarified. It is shown that in the orbital of the in-plane copper and the apex oxygen orbital are occupied by a substantially smaller fraction of holes than the in-plane orbitals, at variance with proposals lending importance to copper-apex oxygen hybridization. At the in-plane oxygen site a sizable admixture is found at the Fermi level of . The in-plane charge distribution of is found to be qualitatively similar to that of the high-temperature tetragonal phase of . It appears that the additional holes are shared among copper and oxygen sites in similar proportions. This is shown to be compatible with the large Emery model provided that the difference between the and atomic energies is comparable to the first neighbor overlap energy.
- Received 26 June 1997
DOI:https://doi.org/10.1103/PhysRevB.57.8590
©1998 American Physical Society