SOME CONSEQUENCES OF THE LAYERED STRUCTURE OF HTSC

The S-N model for high T-c superconductors is briefly described and so me inadequacy is mentioned for BTSC containing no CuO chains between t he CuO2 planes. A theory is presented for the static c-axis conductivi ty and superconductivity for such superconductors and compared with ex perimental data on YBCO with varying oxygen concentration. The basis i s the assumption that the hopping of electrons between the CuO2 planes is due to resonant tunneling through localized centers between the pl anes, and the amplitudes for different centers having the same energy are coherent. The dependence of the normal conductivity on temperature and concentration of resonant centers is calculated. Comparison with experiment shows reasonable agreement. From the obtained dependence of the concentration of resonant centers on the oxygen concentration it can be concluded that these centers disappear simultaneously with hole s in the valence band, and hence both originate from the same impurity states with energies below the top of the valence band, which disappe ar at a certain doping. The supercurrent in the superconducting state proves to be of the Josephson type. The critical value is defined as f unction of temperature and concentration of resonant centers. Its magn itude is estimated to be J(c) similar to 10(5) - 10(7) A/cm(2).