Parametric Amplification of Ultrasound in Strong Magnetic Fields

Abstract

When ultrasound propagates in a piezoelectric semiconductor, the acoustoelectric interaction between the acoustic flux and the conduction electrons leads to parametric amplification of acoustic waves offrequencies different from that of the initial ultrasonic wave. The acousto-electric interaction between the electrons and the ultrasound can be modified by applying a strong magnetic field transverse to the direction of propagation of the ultrasound. The application of the magnetic field is shown to lead to the enhancement of the parametric-amplification process for waves whose frequency lies in the vicinity or below the frequency of maximum linear gain (or loss) in high-mobility semiconductors such as InSb or GaAs. However, the threshold strain necessary to have the parametric amplification exceed the linear loss also increases with magnetic field owing to the large enhancement of the linear electronic losses with magnetic field.