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.