Low-temperature elastic experiments on glasses at very low frequencies

The Grüneisen parameter and the low-frequency elastic loss of vitreous silica, PMMA, and of the metallic glasses PdSiCu, PdZr, and CuZr have been measured between 0.4 K and 6 K using an elasto-caloric technique. The absorption measurements between 5·10^–3 Hz and 30 Hz give further support for the tunneling model in a hitherto poorly investigated domain of relaxation times. New features of the low-temperature behaviour of glasses are a long-time creep and an absorption peak of the metallic glass PdZr nearT_c.Dedicated to K. Dransfeld on the occasion of his 60th birthday