c-Axis Infrared Conductivity of a dₓ₂₋y₂-Wave Superconductor with Impurity and Spin-Fluctuation Scattering

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Results of a calculation of the c-axis infrared conductivity sigmac for a dₓ₂₋y₂-wave superconductor which include both elastic impurity and inelastic spin-fluctuation scattering are presented and compared with the ab-plane conductivity sigmaab in the same model. In this model,the interlayer c-axis coupling is taken to be weak and diffusive. While in clean systems, inelastic scattering leads to a peak at omega = 4*Delta₀ in sigmaab for T < Tc, it has little effect on the corresponding sigmac, which exhibits structure only at omega = 2*Delta₀ and is directly related to the single-particle density of states N(omega). The c-axis penetration depth lambdac in the same model is predicted to vary as T³ at low temperatures in clean samples. We discuss recent optical experiments on the cuprates and compare with these predictions.