Far-Infrared Measurement of the Energy Gap ofV3Si

Abstract

We have measured in the far infrared (2-70 ${\mathrm{cm}}^{-1\mathrm{}}$) the difference between the surface impedances of normal and superconducting ${\mathrm{V}}_3$Si at various temperatures. The radiation was transmitted through a nonresonant cavity containing several single-crystal slabs of ${\mathrm{V}}_3$Si using a lamellar grating interferometer in conjunction with a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-cooled bolometer detector. A vacuum window isolated the detector from the nonresonant cavity. Temperature-dependence measurements have been made up to 30 °K and no change in the surface impedance was observed near the martensitic phase transition at 21 °K. There was a spread in the value of the energy gap, extending, at 4.2 °K, from 12 ${\mathrm{cm}}^{-1\mathrm{}}$ ($2{\Delta }_{min}=1.0\mathrm{}\mathrm{k}{\mathrm{T}}_{\mathrm{c}}$) to 46 ${\mathrm{cm}}^{-1\mathrm{}}$ ($2{\Delta }_{max}=3.8\mathrm{}\mathrm{k}{\mathrm{T}}_{\mathrm{c}}$).