Doppler-Shifted Acoustic Cyclotron Resonance in Gallium

Abstract

The absorption of 260-MHz longitudinal sound waves in single crystals of gallium has been measured at 1.2° K for propagation along the [100] axis. With the magnetic field in the (001) and (010) planes, sharp resonant peaks in the attenuation are observed over a large angular range centered on the propagation axis. Two series of absorption maxima, degenerate in the (010) plane, are attributed to a magnetoacoustic density-of-states resonance of seventh-band electron orbits for which the differential area $\frac{\mathrm{dA}}{d{k}_z}$ is an extremum. The average drift velocity and cyclotron effective mass obtained from the Doppler splitting are compared with corresponding parameters in the nearly free-electron approximation. Other resonances near the [100] axis are identified with seventh- and eighth-band orbits and are correlated with dc size-effect measurements. A Doppler-shifted open-orbit resonance for H·[010] associated with the sixth-band hole surface which permits open orbits in the [001] direction is described. The carrier drift along the sound propagation is obtained from the separation of corresponding subharmonic peaks for $\pm n$.