Magnetoacoustic Attenuation, Open Orbits, and Magnetic Breakdown

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Abstract
A theory of the magnetic-field dependence of the ultrasonic attenuation in metals is given for some simple models of the Fermi surface. These models exhibit open orbits and allow for magnetic breakdown from open to closed orbits. The theory is semiclassical and is based on a generalization of the path-integral method of solving Boltzmann's equation. Results of calculation are given for magnetic fields perpendicular to the sound wave vector q, with both longitudinal and transverse polarizations and with open orbits both parallel and perpendicular to q. These cases include the geometry corresponding to the open-orbit resonance observed experimentally in cadmium by Gavenda and Deaton. It is found that (a) the transverse polarization shows open-orbit antiresonances; (b) experimental evidence of magnetic breakdown can be obtained only by a detailed examination of the whole line shape; (c) quantum-mechanical coherence effects should manifest themselves as an extra set of highly nonsinusoidal oscillations.

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