Acoustic cyclotron resonance and giant high-frequency magnetoacoustic oscillations in metals with locally flattened Fermi surfaces

We consider the effect of local flattening of the Fermi surface (FS) of a metal upon geometric oscillations of the velocity and the attenuation of ultrasonic waves in the neighbourhood of the acoustic cyclotron resonance. It is shown that such peculiarities of the local geometry of the FS can lead to a significant enhancement of both the cyclotron resonance and the geometric oscillations. Characteristic features of the coupling of ultrasound to short-wavelength cyclotron waves arising due to the local flattening of the FS are analysed.