Softening of surface phonons in the (100) plane of Nb3Sn

The propagation of the surface acoustic mode in the (001) plane is investigated as a function of the temperature dependent elastic moduli of Nb₃Sn in the cubic phase. For the 100] and 110]-directions a softening of the surface mode velocity ν_s is found to follow the softening of the velocity ν_T2 of the bulk shear mode T₂A. It is shown that for the 100]-direction the ratio $\text{(}\text{ν}{}_{\mathrm{s}}\text{ν}{}_{\mathrm{T2}}\text{)}$ tends to ?2 at the structural phase transition. The question is discussed of whether the softening of the surface mode can be observed with Brillouin scattering from opaque surfaces.