Build-up of ultrasonic noise and ultrasonic amplification in a bismuth sample subjected simultaneously to an electric and a magnetic field are investigated. The ultrasonic noise is generated in the direction of carrier drift. Under conditions of ultrasonic amplification the quantum resonances of the magneto-acoustic attenuation in Bi are “inverted”, i. e. maxima of attenuation are converted into minima by the application of a suitable electric field. Estimated values of the de-attenuation caused by the electric drift field range around 100 db/cm, the gain referred to the attenuation at zero magnetic field being 22 db/cm for shear waves at 265 Mc/s. Optimum signal amplification corresponds to a minimum of generated ultrasonic noise.
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Klaus Walther (1966) studied this question.