Charge fluctuations in high- tc superconducting cuprates: A reformulation of the “symmetry dilemma” of the mean-field approximation

• Published in: Chemical physics 1989-07, Vol.135 (1), p.27-36
• Main Authors: Böhm, Michael C., Bubeck, Gerd, Oleś, Andrzej M.
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron states; Exact sciences and technology; Physics; Theories and models of many electron systems
• ISSN: 0301-0104
• DOI: 10.1016/0301-0104(89)87003-X

We investigate the strength and symmetry-dependence of the mean-square deviation of the electronic charge in a Cu 12O 17 10− cluster which has been used as a model for the CuO 2 plane of the recently discovered high- T c superconducting copper oxides. The charge fluctuations are derived in the mean-field (|φ SCF>) and the correlated ground state (|Ψ o>), respectively. The interatomic correlations in the cuprate cluster are described by modifying |φ SCF> obtained in a semi-empirical SCF formalism via the “local approach”. A comparison of the mean-field data and the correlated ones leads to a physically transparent alternative formulation of the “symmetry dilemma” of the restricted Hartree-Fock approximation. The mean-field errors in the simulation of the charge fluctuations are largest in the limit of highly symmetric wavefunctions. Electronic correlations lead here to a sizeable charge localization with the largest effect in the Cu 3d x2−y2 orbitals. Our results show that the high- T c superconducting oxides belong to the class of strongly correlated systems with fluctuating valences. They are furthermore characterized by a strong coupling of local phonons (breathing mode) to the redistribution of the hole density and to changes in electron correlations.