The nature of insulator-metal transition and the mechanism of carrier generation in doped high-Tc superconductors

Abstract

It is proposed that the local atomic complexes consisting of two adjacent cations (Cu or Bi) with intermediate O-ion and having-U-center properties are formed in high-Tc superconductors (HTSC) at the certain concentration of localized doped carriers. The pair level of arising-U-centers lies at the top of the fulfilled oxygen valence band. Such type of electronic structure is supposed to be responsible for unusual properties of HTSC. The broad outline of HTSC doping process is sketched. It is supposed that doped carriers are well localized at least for small doping concentration while the mobile hole carriers result from the transfer of a part of electrons from the oxygen band to-U-centers. In the framework of proposed model the dielectric-metal transition and the evolution of HTSC properties with doping can be understood.