Anomalous attenuation of the ultrasonic waves in n-InSb in a pinched plasma state

A few years ago Tanaka and others of our group reported that the longitudinal ultrasonic waves travelling along the <110> direction in n-InSb sample were anomalously attenuated when it was in a pinched plasma state under a strong electric field applied along this direction (K. Tanaka et al.: Phys. Letters 39 A (1972) 43). They examined various possible causes of dumping qualitatively and concluded that this might be the Akhieser loss due to the raise in temperature of the sample caused by the pinch effects. We applied the DAJ theory to this problem and calculated the radial variations of the carrier density and the temperature in the InSb sample. It was found that there is no such large temperature raise over a wide region of the sample to cause Akhieser loss as large as the observed attenuation. We further measured the frequency dependence of the attenuation and found that it seems to be of the form ωsup(n) with n=4 in the low frequency region and with n asymptotically equals 1 in the high frequency region, when the dc pulse was over 60 A. Taking into account these theoretical and experimental findings we must look for some causes for this dumping other than the Akhieser loss, such as diffraction loss due to inhomogeneity in elastic properties due to the thermal gradient in the sample. (auth.)