Temperature dependence of the phonon frequencies in Nb3Sn and V3Si
Gor'kov L.P. , Dorokhov O.N.
The softening of the phonon frequencies, which was observed in [1*23 for a wide interval of wave vectors, is explained using the model of [3) with two peaks in the state density, under the assumption that the Fermi level is located near one of the peaks. The proximity of the sample to the martensitic transition favors superconductivity, since this proximity reflects the proximity of the chemical potential to the position of one of the peaks.