Electronic Raman Scattering by Superconducting-Gap Excitations inNb3Sn andV3Si

Raman-scattering measurements on ${\mathrm{Nb}}_3$Sn and ${\mathrm{V}}_3$Si show new peaks in the superconducting state close in energy to the superconducting gap $2\Delta$. These are attributed to direct electronic Raman scattering by pairs of superconducting quasiparticles. A theory is presented which fits the data well and provides evidence for anisotropy of the gap (∼20% in ${\mathrm{Nb}}_3$Sn) and of the matrix element for electronic Raman scattering.