The role of intermediate layers in the c-axis conductivity of layered superconductors

A simplified model of c axis transport in the high T_c superconductors is presented. Expressions are found for the c axis optical conductivity, the d.c. resistivity, and the c axis penetration depth. Within the framework of this model, the pseudogap in the optical conductivity arises naturally as a result of the layered band structure of the high T_c materials. We discuss the occurence of the pseudogap in terms of three parameters: a band gap Delta_{ps}, a temperature dependent scattering rate Gamma(T), and the strength of the interlayer coupling t_{perp}. We are also able to find analytic expressions for the d.c. conductivity and the low temperature penetration depth in terms of these three parameters. This work is an attempt to present a simple, unified picture of c axis properties in the high T_c cuprates.