Magnetoacoustic Wave in an Electron-Hole Gas—Bismuth

This paper presents an experimental study in bismuth of the acoustic plasma wave at microwave frequencies. We have studied the coupling, in the presence of a dc magnetic field, of this wave to the Alfvén mode; experiments have been performed at two frequencies: 10 and 3 GHz. The 3-GHz transmission spectrometer devised by the authors shows very clearly the presence of the magnetoacoustic mode, while at 10 GHz hybrid and cyclotron resonances are mixed with the phenomenon studied. The electromagnetic theory of this phenomenon in the case of collisionless isotropic plasma is recalled; the case of bismuth is then fully analyzed and compared with experiment. From the coupling of the two modes, $n{\epsilon }_0$ is obtained, where $n$ is the carrier density and ${\epsilon }_0$ the band overlap.