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

Abstract

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 $P{\ensuremath{\gamma}}^{2}$ (where P is the TS density of states and $\ensuremath{\gamma}$ is the phonon-TS coupling) is close to the one in metallic glasses. The crossover temperature from the ${T}^{3}$ law to the plateau regime in the attenuation is well defined. Hence, within the TS model, both P and $\ensuremath{\gamma}$ can be calculated. The TS's seem to be intrinsic to the quasicrystal structure.