Acoustic measurements of crystalline aluminum and of an aluminum alloy (Al 5056)

Abstract

We present vibrating reed experiments of aluminum with various degrees of disorder at a measuring frequency of 2.5 kHz and in the temperature range between 30 mK and 300 K . Evidence for the existence of ‘glass-like’ two-level tunneling systems is only observed for a poly-crystalline sample. The internal friction Q −1 of a single crystal is almost temperature independent between 30 mK and 1 K and has a maximum around 7 K which we attribute to the thermally activated motion of dislocations. Q −1 of our Al 5056 specimen is more than an order of magnitude smaller than that of the aluminum single crystal.