MODEL FOR C-AXIS RESISTIVITY OF CUPRATE SUPERCONDUCTORS

On the basis of the structural features and correlation effects that e xist in the cuprate systems it has been argued that the Cu 3d(3z2-r2) orbitals are reasonably well suited for the transport along the c axis . On the same ground it has also been argued that the band of the out- of-plane states that involves the Cu 3d(3z2-r2) orbitals lies higher t han the occupied in-plane states by an amount W(n) that decreases with the carrier density (n) so as to vanish beyond a certain critical con centration no. Phenomenological arguments are used to obtain expressio ns for rho(c) within the Boltzmann framework for all n. When n<n(0), r ho(c) shows a semiconducting behavior for T<W and a metallic behavior for T>W. For n>n(0) it turns out that rho(c) is metallic for all T. Th e observed temperature dependence of rho(c) is explained reasonably by the present model for a number of samples of La2-xSrxCuO4, YBa2Cu3P7- y, and Bi2Sr2-xLaxCuOy with different dopings. The values of W(n) esti mated for these samples support one of the main features of our model that this gap W(n) decreases with increasing n.