Acoustical Plasmons, Phonon Anomalies, and Superconductivity in Transition-Metal Systems

It is shown that the concept of acoustical plasmons may be useful for understanding the anomalous behavior of the phonon dispersion curves of superconducting transition-metal systems with high $T_c$ (5-10°K). The value of the velocity of plasmon sound obtained from the phonon calculations for Nb is quite close to that needed to explain the specific-heat anomaly by the acoustical-plasmon mechanism.