FERMI-SURFACE AND FINE-STRUCTURE OF THE PHONON-DISPERSION CURVES OF WHITE TIN

Acoustic phonon-dispersion curves in white tin are precisely measured by inelastic neutron scattering. Phonon group velocities for each of the measured branches are derived and the observed fine structure in the phonon spectrum is analyzed in terms of Kohn-type and other anomalies arising from electron-ion interactions in the metal. It is concluded that, in spite of relatively small absolute deviations of the real Fermi surface from the Fermi sphere, the complicated topology of the Fermi surface must be considered to explain the totality of the existing anomalies including the effect of ''Kohn anomaly in sound''.