Conductivity of icosahedral Al-Pd-Re at ultralow temperatures

The low-temperature electrical conductivity sigma(T) has been studied for four samples of icosahedral Al70.5Pd21.0Re8.5 in the form of annealed ingots. The resistance ratios R = rho(4 K)/rho(295 K) were in the range 70-180. The overall temperature dependence of the conductivity below 1 K is stronger than for previously reported results and the conductivity is lower. Two samples were measured down to 15 mK and two down to 0.1 mK. For the latter samples sigma(T) attained constant finite values at the lowest temperatures. A variable-range-hopping mechanism is discussed. It is concluded that the conjecture for a metal-insulator transition in i-AlPdRe remains unresolved and that measurements must include temperatures below 15 mK on samples of higher residual resistance ratios to settle this problem. [S0163-1829(99)08039-X].