HOLE LOCALIZATION, ELECTRONIC-STRUCTURE AND HIGH-T-C SUPERCONDUCTIVITY

It is shown that the dielectric gap in the electronic spectrum of oxid e high-T-c systems appears because of ordering arrays of localized (he avy) holes or the charge density waves. Dielectric-metal (DM) phase tr ansitions in these systems are the consequence of impurity bands appea ring at doping, delocalization of the ordered heavy holes located on t he metal-apical ion bonds. The free carriers introduced by doping can couple through excitation of these localized holes. This leads to high -T-c superconductivity with small coherence length and anomalous tempe rature dependence of H-c2(T). These results were obtained on the basis of experimental studies of specific heat, magnetic properties, therma l expansion and other characteristics. The physical nature of the obse rved DM transitions and negative thermal expansion in HTSC systems are discussed.