Interaction of an acoustic wave with electrons on a flat spot of the Fermi surface: I. Normal metals

A theoretical and experimental study of the electron contribution to the attenuation (α/q) and velocity (Δs/s) of a longitudinal acoustic wave in high-purity gallium is reported. The observed anomalies of the temperature and angular dependences of α/q and Δs/s are attributed to the existence of a flat spot on the Fermi surface, localized in the sixth valence band. It is shown that the resonance singularities of the strain contribution to the sound attenuation and velocity are completely compensated in the frequency interval f ≤ 250 MHz by solenoidal electromagnetic fields accompanying the propagation of sound in the metal. It is predicted theoretically that a weakly attenuated electromagnetic “beam” wave can be excited by a hypersonic field in a normal metal in the absence of a magnetic field.

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