Far-Infrared Absorption in Superconducting Lanthanum

Abstract

Measurements have been made of far-infrared absorption in pure, face-centered cubic, superconducting lanthanum at 1.3°K. The results indicate a gap width $2\Delta =12.0\mathrm{}\pm 1.0$ ${\mathrm{cm}}^{-1\mathrm{}}$. In terms of the measured value of the critical temperature, $T_c=6.06\mathrm{}°$K, $2\Delta =2.85\mathrm{}\pm 0.24k{T}_c$. The data indicate the possible presence of a small amount of structure in the absorption curve at an energy about twice the gap width. These results are compared with theoretical predictions which have been made recently from a proposed new mechanism for superconductivity in lanthanum.