Far IR Spectra of Ceramic Superconductors

We compare our measurements of structure in the reflectivity near the superconducting energy gap on a series of samples of La-Sr-Cu-O and Y-Ba-Cu-O superconductors with those of four other groups. We present a semiquantitative fit to the data in the normal and superconducting states using a phenomenological model which includes the Mattis-Bardeen theory in the dirty limit, effective medium theory and anisotropy. We find fits which yield superconducting gaps both smaller and of the order of those measured by tunneling, depending upon materials parameters.