Landau Quantum Oscillations of the Velocity of Sound in Be: The Strain Dependence of the Fermi Surface

Abstract

Landau quantum oscillations of the velocity of sound in Be are reported. A general thermodynamic relation between the quantum oscillations of the velocity of sound (elastic moduli) and the strain dependence of the Fermi surface is given and is used to interpret the results. This relation shows that the amplitude of the oscillations is determined by the magnetic susceptibility and the strain dependence of the Fermi-surface extremal areas. An oscillatory as well as a monotonic Alpher-Rubin effect is obtained in this treatment. All major features of this theoretical result are generally verified in the experimental results. The strain dependence of the Fermi surface obtained in this work is in susbtantial agreement with previous hydrostatic pressure studies. At low temperatures, magnetic interaction effects modily the oscillation pattern. These results imply that the (differential) susceptibility at high frequencies is never paramagnetic. This behavior is shown to be consistent with the presence of magnetic domains whose walls are immobile at the sound frequency. Experimental techniques are also presented.