NORMAL STATE OF STRONGLY COUPLED ELECTRONS AND PHONONS - DIELECTRIC-PROPERTIES, VIBRATIONAL EXCITATIONS AND APPLICATION TO HIGH-TC SUPERCONDUCTING METAL-OXIDES

A new theory of many-body phenomena in a strongly coupled electron-phonon system is developed, taking into account the polaron collapse of the electron band and the instability of the phonon vacuum. A "lambda(-1)" expansion and multi-phonon diagram technique are developed to obtain the dielectric response function and new vibrational excitations. Static and dynamic responses show unusual temperature, q and omega-dependences. Phonons mix with polaronic plasmons thus forming new excitations - "plasphons". A microscopic model of the anomalous extra modes, observed in neutron scattering experiments in metal oxides is proposed. The relevance of the polaron theory of high-T(c) superconductivity to high-T(c) oxides is discussed in view of some recent experimental results. The charged Bose-liquid ground state (small bipolarons) is claimed to be relevant to describe some normal and superconducting state properties of metal oxides.