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 P g amma(2) (where P is the TS density of states and gamma is the phonon-TS cou pling) is close to the one in metallic glasses. The crossover temperature f rom the T-3 law to the plateau regime in the attenuation is well defined. H ence, within the TS model, both P and gamma can be calculated. The TS's see m to be intrinsic to the quasicrystal structure.