Charge fluctuations and superconductivity in superconducting oxides

To understand the mechanism for superconductivity in the superconducting oxides we investigate charge and spin fluctuations on the CuO₂ plane in the crystals. The Coulomb interaction between d electrons on the Cu sites and the Coulomn interaction between d and p electrons on the neighboring sites are taken into account. The Coulomb interaction strongly enhances the charge fluctuations in the low energy region and the charge fluctuations exceed the spin fluctuations when the d and p electron levels are close to each other.