LATTICE AND SPIN BIPOLARONS IN METAL-OXIDES AND DOPED FULLERENES

We extrapolate the BCS theory to the strong electron-phonon and (or) e lectron-spin fluctuation interaction and show that in the strong-coupl ing limit the ground state is a charged Bose liquid of lattice and (or ) spin bipolarons. Kinetic and thermodynamic properties of charged bos ons on a lattice in the normal and superconducting states are discusse d, and some evidence for the model is given from NMR, neutron scatteri ng, near-infrared absorption, Hall effect, resistivity, thermal conduc tivity, isotope effect, heat capacity, and critical magnetic fields of high-T(c) oxides. The maximum attainable T(c) is estimated to be in t he region of the transition from the Fermi liquid to a charged Bose li quid (polaronic superconductivity). The proposed theory is not restric ted by low dimensionality and might be applied to cubic oxides such as the ''old'' BaPbBiO and to alkali-doped C60 as well.