Intensity-dependent ultrasonic attenuation in a metallic glass at low temperatures

Abstract
The attenuation of 720 MHz transverse acoustic waves has been studied in the metallic glass Pd0.775Si0.165Cu0.06 at low temperatures. At 0.062 K the attenuation is found to be intensity-dependent, a behaviour already observed in amorphous insulators and explained by the existence of a broad distribution of two-level systems. The temperature variation of the attenuation has been measured between 0.062 K and 1.5 K at low and high acoustic intensities. It is described by a resonant interaction with two-level systems plus a relaxation contribution of the form AωT + Bω2 log T/ T0