Tunneling states in a single-grain Al-Cu-Fe quasicrystal

Velocity and attenuation of acoustic waves (190 Mhz) have been measured in a phason-free single grain of i-AlCuFe between 40 mK and 30 K. The results reveal the existence of tunneling states (TS's). The coupling parameter Pγ² (where P is the TS density of states and γ is the phonon-TS coupling) is close to the one in metallic glasses. The crossover temperature from the T³ law to the plateau regime in the attenuation is well defined. Hence, within the TS model, both P and γ can be calculated. The TS's seem to be intrinsic to the quasicrystal structure.