STRONG-COUPLING SUPERCONDUCTIVITY AND HIGH-T-C PHENOMENON

Small-polaron and bipolaron formation destroys the Fermi-liquid behavi our of carriers strongly coupled with phonons or spin fluctuations. Th e non-adiabatic motion of self-trapped carriers results in the fundame ntal difference of low-mobility conductors compared with simple metals and Bardeen-Cooper-Schrieffer supercondutors. An appealing explanatio n of many properties of high-T-c cuprates and doped fullerenes emerges if one applies the polaron theory of strong-coupling superconductivit y. The microscopic theory of the inplane and 'c'-axis transport in cup rates is proposed. The temperature and doping dependence of the in-pla ne and out-of-plane resistivity, the Hall effect and the spin suscepti bility is shown to be in a remarkable agreement with the experimental data in underdoped, optimally doped and overdoped La2-xSrxCuO4 for the entire temperature regime. The normal state gap is explained and its doping and temperature dependence is clarified. The resonance Wigner s cattering of small bipolarons in a random potential leads to logarithm ically divergent low-temperature resistivity as observed for several c uprates. The interaction responsible for high T-c values is elucidated .