Comparison of Optical Spectra of Planar Superconductors

We have made a comparison of the optical spectra of crystals of Ba sub 2 YCu sub 3 O sub (6+x), for several values of x, of La sub (2-y) Sr sub y Cu sub 3 O sub 4, for several values of y, of NbSe sub 2, and of Ba sub 2 Sr sub 2 CaCu sub 2 O sub x. In all cases we have measured the conductivity and dielectric constant of individual crystals in the planar directions over the frequency range from the far-infrared to the visible and over the temperature range from room to liquid He. We have focused particularly on systematic deviations of the spectra from behavior expected for a frequency independent mass and relaxation rate.