EFFECTIVE ONE-BAND ELECTRON-PHONON HAMILTONIAN FOR NICKEL PEROVSKITES

Inspired by recent experiments on the Sr-doped nickelates, La2-xSrxNiO 4, we propose a minimal microscopic model capable of describing the va riety of the observed quasistatic charge/lattice modulations and the r esulting magnetic and electronic-transport anomalies. Analyzing the mo tion of low-spin (s=1/2) holes in a high-spin (S=1) background as well as their coupling to the in-plane oxygen phonon modes, we construct a sort of generalized Holstein t-J Hamiltonian for the NiO2 planes, whi ch contains, besides the rather complex ''composite-hole'' hopping par t, nonlocal spin-spin and hole-phonon interaction terms.