Acoustic properties of amorphous PdSiCu at very low temperatures

Abstract

We have studied in detail the temperature and strain dependence of the acoustic properties of the metallic glass PdSiCu in the temperature range 0.2 mK ⩽T⩽ 200 mK with the vibrating reed technique at 980 Hz. At very low temperatures the sound velocity variation Δ v/ v deviates from the expected logarithmic dependence with increasing acoustic intensity. Strikingly, the internal friction Q −1 shows also a logarithmic decrease with decreasing temperature, instead of the plateau predicted in the kHz range by the standard tunneling model. We show that the extrapolated data to zero strain unveil the behaviour expected within the tunneling model.