SPIN AND CHARGE BIPOLARON KINETICS OF HIGH-Tc SUPERCONDUCTORS

Abstract

We extend the BSC theory to the strong electron-phonon (magnon) coupling limit. We show that the formation of small polarons and bipolarons provides a number of new physical phenomena both in the normal and superconducting states and explains low-energy physics of high-Tc superconductors. Both lattice and spin (bi)polarons are discussed. A highly nonadiabatic motion of bipolarons leads to a unique physical nature of (bi)polaronic superconductivity, making it totally different from that of the BCS one, including its wellknown strong-coupling generalization. The maximum attainable Tc is estimated to be in the region of the transition from the Fermi-liquid to a charged Bose-liquid. Some evidence for 2e bosons is given from NMR, neutron scattering, near-infrared absorption, Hall effect, resistivity, thermal conductivity, and critical magnetic fields of high-Tc oxides. An infinite thermal conductivity of two-dimensional charged bosons is predicted below Tc. The insulator-metal transition and ARPES in copper oxides are also discussed. The proposed theory is not restricted by low dimensionality and might be applied to cubic oxides like BaPbBiO and to alkali-doped C 60.