Low-temperature thermal conductivity of icosahedral Al63Cu25Fe12 and Al62Cu25.5Fe12.5 quasicrystals

We present measurements of thermal and electrical conductivity of icosahedr al Al63Cu25Fe12 and Al62Cu25.5Fe12.5 quasicrystals in the temperature range 0.1-6 K. Electrical conductivity Delta sigma (T)=sigma (T)-sigma (4.2 K) o f Al63Cu25Fe12 contrary to aa(T) of Al62Cu25.5Fe12.5 shows a linear increas e with rootT up to 2 K, as predicted by electron-electron interaction theor ies, followed by a strong change of regime at around 2 K. Low-temperature p honon thermal conductivity, kappa (ph)(T), Of Al63Cu25Fe12 shows a deviatio n from the expected T-3 law: in the T-range 0.1-0.8 K, kappa (ph)(T)similar toT(2.7). An anomaly in phonon thermal conductivity appears near 1 K, whic h superposes to the monotonous increase of kappa (ph)(T) With T obeyed up t o higher T. We suppose that the origin of this anomaly in phonon thermal co nductivity is related to the strong change of the regime in the variation o f the Delta sigma (T), which appears in the same temperature range. For Al6 2Cu25.5Fe12.5, kappa (ph)(T) varies almost linearly between 0.28 and 1.2 K, and exhibits a crossover towards a very rapid variation below 150 mK, much more rapid than T-3. There is no evidence for phase transitions from speci fic heat measurements in the temperature range of the crossover of kappa (T ). (C) 2000 Elsevier Science B.V. All rights reserved.