Magnetoacoustic Effects in Tilted Magnetic Fields

Abstract

We have shown for the cases of a free-electron gas, the two-spherical-band model, and the model of majority and minority carriers that certain portions of the Fermi surface can be mapped in detail. This can be done by using geometric resonances in the sound attenuation in tilted magnetic fields, and the drift velocity of the carriers along the magnetic field can simultaneously be determined. For this to be possible, $\omega \tau$ must exceed unity and the Fermi velocity must not exceed the sound velocity by more than a factor of 100. Then the diameters of all the orbits, not merely the extremal orbits, can be measured and the drift velocity along the magnetic field determined as well. The general features of the phenomena considered do not prove dependent on the particular models used in our calculations. In addition to the results specifically pertaining to tilted fields, we have found that when the assumptions of equal effective masses and relaxation times are dropped for a two-band model of a semimetal, the contribution of the two types of carriers to the ultrasonic absorption is additive. On examining the contribution to the absorption for a model of majority and minority carriers, we have found, also, that the minority carriers dominate the attenuation when they are in the region of geometric resonances.