Electron Relaxation Time from Magnetoacoustic Oscillations and the Tilt Effect

Several ultrasonic techniques for measuring electron relaxation time $\tau$ in a metal or semimetal are described. Two methods involve the variation in the peak-to-peak attenuation of geometric resonance oscillations in a decreasing magnetic field. The third involves attenuation peaks in the tilt effect, and the fourth involves the low-field disappearance of Landau-level oscillations in the tilt effect. The methods were applied to data taken in Bi at an ultrasonic frequency of 9.3 GHz. For the directions studied in our sample, ${\omega }_s\tau$ ranged from 0.175 to 0.30. It is suggested that the first method can be applied to existing magnetoacoustic data.