Role of charge-density fluctuations and many-particle Coulomb correlationsin the mechanism of high-temperature superconductivity of cuprate metal-oxide compounds

The charge-fluctuation (plasmon) mechanism of d-wave Cooper pairing in high -T-c superconductors (HTSCs) is considered. This mechanism arises from the interaction of current carriers with collective low-frequency electron-dens ity excitations. It is shown that for layered crystals of cuprate metal-oxi de compounds the existence of a one-electron spectrum of anisotropic extend ed saddles (flat bands) with an anomalously high density of states can give rise to damped long-wavelength charge-density fluctuations that lead to su ppression of the static screened Coulomb repulsion in the region of small m omentum transfers. As a result, an effective attraction between electrons a rises in the d-wave Cooper channel; this attraction is substantially enhanc ed by many-particle Coulomb correlations of the local-field-effects type, d escribed by a Coulomb vertex Gamma (c). It leads to Cooper pairing with d(x 2-y2) symmetry of the superconducting order parameter and can make for rath er high maximum values of the critical temperature, T-c similar to 100 K, a t the optimum doping level for cuprate metal-oxide compounds. Taking the an isotropy of the electron-phonon interaction into account makes it possible to describe the weak oxygen isotope effect in HTSC compounds. (C) 2001 Amer ican Institute of Physics.