Effects of Energy-Band Structures on Longitudinal Magnetoacoustic Phenomena in Bismuth

Abstract

The effects of energy-band structures on the propagation of ultrasound in bismuth in the presence of a dc magnetic field are investigated by using the quantum-mechanical treatment which is valid in the high- frequency region. It is found that the absorption coefficient and change in sound velocity oscillate with the dc magnetic field for the Cohen nonellipsoidal nonparabolic (NENP) model. However, no oscillations in the absorption coefficient can be observed in strong magnetic fields for both ellipsoidal nonparabolic (ENP) and ellipsoidal parabolic (EP) models. These oscillations can be interpreted as the so-called "giant quantum oscillations"which arise from the resonant absorption of the sound wave by electrons. It is also found that the absorption coefficient and change in sound velocity increase with the sound frequency for NENP, ENP,and EP models. However, there exsits a big discontinuous cusp at the high-frequency region for both ENP and EP models. Therefore we conclude that the NENP model will give a much better description of the energy band structure in bismuth than do the ENP and EP models.