Physica B: Condensed Matter 219-220, 247 (1996)

P. Esquinazi, R. König, F. Pobell

Abstract

With mechanical oscillators we have studied the velocity of sound and sound attenuation of solids it acoustic frequencies and at milli- and microkelvin temperatures. We find that the acoustic properties of amorphous solids show significant deviations from the predictions of the standard tunneling model. In addition, we show that the acoustic properties of polycrystalline normal conducting metals and superconductors resemble closely those of amorphous materials, demonstrating the “universality of glass-like behaviour” and questioning our present understanding of “disorder”. The observed properties do not seem to be influenced by the presence of conduction electrons.