Model for c-axis resistivity of cuprate superconductors

Abstract

On the basis of the structural features and correlation effects that exist 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 than 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 concentration n₀. Phenomenological arguments are used to obtain expressions for ρc within the Boltzmann framework for all n. When n<n₀, ρ_c shows a semiconducting behavior for T<W and a metallic behavior for T>W. For n>n0 it turns out that ρ_c is metallic for all T. The observed temperature dependence of ρ_c is explained reasonably by the present model for a number of samples of La_2-xSr_xCuO₄, YBa₂Cu₃O_7-y, and Bi₂Sr_2-xLa_xCuO_y with different dopings. The values of W(n) estimated for these samples support one of the main features of our model that this gap W(n) decreases with increasing n.