UC Irvine

We report measurements of the Eg optical phonon in V3Ge, V3Si, and Nb3Sb, and of the T2g optical phonon in Nb3Sb measured from 9 to 400 K. The Eg optical phonon in V3Ge has an anomalous width, shape, and temperature dependence, similar to that seen in V3Si and Nb3Sn. Both the Eg and T2g optical phonons in Nb3Sb, on the other hand, show no anomalous behavior and can be understood in terms of simple anharmonic interactions. We point out the existence of a linear correlation between the magnetic susceptibility and the Eg phonon linewidth for V3Si, V3Ge, and Nb3Sn. Scaling arguments show that the Eg phonon linewidth of these three compounds exhibits very similar temperature dependences, with the remaining small differences yielding information concerning the distribution of the joint electronic density of states with respect to the Fermi level. These anomalies are attributed to coupling of the Eg phonon to interband electronic transitions between the flat bands emanating from the 12 level. A simple model of the interaction quantitatively reproduces the temperature dependence of the Eg phonon linewidth. © 1983 The American Physical Society.