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

We present measurements of thermal and electrical conductivity of icosahedral Al63Cu25Fe12 and Al62Cu25.5Fe12.5 quasicrystals in the temperature range 0.1–6 K. Electrical conductivity Δσ(T)=σ(T)−σ(4.2 K) of Al63Cu25Fe12 contrary to Δσ(T) of Al62Cu25.5Fe12.5 shows a linear increase with T up to 2 K, as predicted by electron–electron interaction theories, followed by a strong change of regime at around 2 K. Low-temperature phonon thermal conductivity, κph(T), of Al63Cu25Fe12 shows a deviation from the expected T3 law: in the T-range 0.1–0.8 K, κph(T)∼T2.7. An anomaly in phonon thermal conductivity appears near 1 K, which superposes to the monotonous increase of κph(T) with T obeyed up to higher T. We suppose that the origin of this anomaly in phonon thermal conductivity is related to the strong change of the regime in the variation of the Δσ(T), which appears in the same temperature range. For Al62Cu25.5Fe12.5, κph(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 T3. There is no evidence for phase transitions from specific heat measurements in the temperature range of the crossover of κ(T).