High temperature superconductivity and charge segregation in a model with strong long-range electron-phonon and Coulomb interactions

An analytical method of studying strong long-range electron–phonon and Coulomb interactions in complex lattices is presented. The method is applied to a perovskite layer with anisotropic coupling of holes to the vibrations of apical atoms. Depending on the relative strength of the polaronic shift Ep and the inter-site Coulomb repulsion Vc, the system is either a polaronic Fermi liquid, Vc>1.23Ep, a bipolaronic superconductor, 1.16Ep