Low temperature calorimetric investigation of an insulating icosahedral Al-Pd-Re quasicrystal

We report on a very low temperature heat capacity investigation of an icosa hedral Al-Pd-Re sample which, from resistivity measurements, is believed to lie on the insulating side of a metal-insulator (M-I) transition. Our main results are: (i) The electronic contribution, which possibly obeys a gamma T variation above 1 K, follows a power T-a law (a approximate to0.1) below 1 K, in agreement with early results obtained for systems crossing the M-I transition. Here T denotes the absolute temperature. (ii) The large nuclear hyperfine contribution of quadrupolar origin, dominant below 300 mK, can o nly be due to the Re nuclei. We reach this conclusion from a comparative st udy of icosahedral Al-Cu-Fe and Al-Pd-Mn quasicrystals. In addition, from t he study of the thermal relaxation of the sample after a heat pulse, we are able to estimate the relaxation times T-1 of the different kinds of nuclei , for those which relax during our experimental time span. (iii) We finally propose a microscopic origin of the quadrupolar-electric field-gradient on the nuclei in terms of local electronic density and atomic structure. (C) 2000 Elsevier Science B.V. All rights reserved.