Amplification of sound in many-valley anisotropic conductors

We obtain a criterion for the amplification of sound in many-valley anisotropic conductors. Calculations for the particular case of strong magnetic fields and low temperatures (Ωcτ = (eH/m*c) ≫l) for a compensated conductor with a given Fermi surface are extended to the general case of M electron and N hole valleys. It is shown that when an electric field is parallel to the displacement vector of the elastic wave and H = 0, the possibility of sound amplification by the electron-hole plasma is determined by the inequality ql > 1. Under the above conditions the sound absorption coefficient is independent of the drift velocity for ql < 1, and this can be used as a diagnostic for electron-hole compensation in conductors.

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