TRANSMISSION OF FAR-INFRARED RADIATION THROUGH THIN FILMS OF SUPERCONDUCTING AMORPHOUS BISMUTH AND GALLIUM AND BETA-PHASE GALLIUM

The ratio TsTn of the far-infrared radiation transmitted through a thin film in the superconducting state to that transmitted through it in the normal state has been measured at 1.1°K for thin-film samples of amorphous bismuth and gallium and samples of partially annealed (β-phase) gallium. The transition temperature Tc of each film was also measured. The sample thicknesses were approximately in the range 50-200 . Numerical calculations based on the strong-coupling theory of superconductivity and on tunneling data produced theoretical values of TsTn which were in reasonably good agreement with the experimental results. The only adjustable parameter was the energy-gap width 2Δ0. The quantities Tc and 2Δ0 decrease with increasing film resistance. The shift in Tc has been previously observed by Naugle and Glover in amorphous bismuth and gallium. The abrupt resistance change in these materials at about 19°K, which is characteristic of thicker amorphous films, appeared instead as a more gradual change in resistance beginning at higher temperatures. © 1969 The American Physical Society.