Is there a metal–insulator transition in the quasicrystalline phase i-Al–Pd–Re?

We discuss measurements of the electrical conductivity σ performed at very low temperature on highly resistive ribbons of the i-Al–Pd–Re phase. Between 1 K and 20 mK, we observe a drop in σ, and the curvature gets stronger and stronger as T tends to zero. Below 20 mK, the samples show signs of insufficient thermalisation. This σ drop can be well described by Mott’s law σ(T)=σ0 exp[−(T0/T)1/4] but the extracted parameter T0 is quite different from other studies on i-Al–Pd–Re. We show that T0 strongly depends on the temperature range of the analysis. Here, the insulating character of the samples is determined using the divergence of the logarithmic derivative of σ, i.e. d ln σ(T)/d ln(T), at low temperature.