ON THE C-AXIS CONDUCTIVITY AND SUPERCONDUCTIVITY OF YBA2CU3OX AS FUNCTION OF X

A theory is presented of the static c-axis conductivity and supercondu ctivity of the YBCO state with varying oxygen concentration. The basis of the theory is the assumption that the hopping of electrons between the CuO2 planes is due to resonant tunneling through localized center s between the planes, acid the amplitudes for different centers with t he same energy are coherent. The dependence of the normal conductivity on temperature and concentrations of the resonant centers is calculat ed. Comparison with recent systematic determinations of the temperatur e-dependent conductivity at different oxygen concentrations shows reas onable 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 holes in the valence band , and hence both originate from the same impurity states with energies below the top of the valence band, which disappear at a certain dopin g. The supercurrent in the superconducting state proves to be of the J osephson type. The critical value is defined as a function of temperat ure and concentration of resonant centers. Its magnitude is estimated to be J(c) similar to 10(5)-10(7) A/cm(2).