Tunneling systems in quasicrystals.

We have measured the low frequency sound velocity and damping of both the icosahedral and crystalline phases of Al sub (74) Si sub 6 Mn sub (20), Mg sub 3 Zn sub 3 Al sub 2, and Al sub 5 Li sub 3 Cu below 1 K. Both the normal metallic quasicrystal i-Al sub 5 Li sub 3 Cu and the superconductor i-Mg sub 3 Zn sub 3 Al sub 2 contain atomic tunneling systems with densities of states a few times smaller than those found in metallic glasses. Since we have found that crystalline phases of these compounds may also contain tunneling systems, we propose that the tunneling systems in quasicrystals are characteristic of unequilibrated materials in general, rather than due to peculiarities of the quasicrystal structure.