Far-infrared transmission of superconducting KxC60 films.

Far-infrared transmission measurements have been performed on normal and superconducting K x C 60 films on Si substrates. The films are prepared by thermal sublimation followed by in situ doping in a vacuum-tight cell. The observed peak in the ratio of the superconducting to normal transmittance near 50 cm -1 is consistent with a distribution of superconducting gaps in the range (2-5)κTc