title: Tunneling state anisotropy in a single grain decagonal quasicrystal.
abstract: We present low-temperature measurements, between 20 mK and 20 K, of the sound velocity variations in a single grain of the decagonal quasicrystal Al-Ni-Co. We have used acoustic shear waves of frequency 70 MHz propagating in the quasicrystalline planes with two different polarizations: parallel and perpendicular to the quasicrystalline planes. Our results show the presence of tunneling states (TSs) with a strong difference of the phonon-TS coupling for the two polarizations, which reveals a strong anisotropy of distribution of the orientations of the TSs in the sample. This result gives direct evidence that TSs are generated by the quasicrystalline structure itself.
authors.affiliation: Laboratoire de Physique des Solides, Université Paris-Sud, Bâtiment 510, 91405 Orsay, France.
authors.forename: F
authors.initials: F
authors.lastname: Bert
authors.forename: G
authors.initials: G
authors.lastname: Bellessa
authors.forename: B
authors.initials: B
authors.lastname: Grushko