Influence of the Superconducting Energy Gap on Phonon Linewidths inNb3Sn

Abstract

Inelastic neutron scattering, used to study acoustic phonon linewidths in ${\mathrm{Nb}}_3$Sn, has revealed abrupt changes in certain phonon lifetimes in the vicinity of the superconducting transformation temperature, $T_c=18.3\mathrm{}°$K. This behavior arises because phonons with energy less than that of the temperature-dependent superconducting gap energy, $2\Delta \mathrm{}\left(T\right)\mathrm{}$, are energetically incapable of decaying by excitation of electron-hole quasiparticle pairs. These measurements give $2\Delta \mathrm{}\left(0\right)=4.4\mathrm{}{k}_{\mathrm{B}}{T}_c$ and reveal a strong anisotropy in the electron-transverse phonon interaction.