SEMICONDUCTOR-LIKE TRANSPORT IN HIGHLY ORDERED AL-CU-RU QUASI-CRYSTALS

The electrical conductivity and Hall effect of Al-Cu-Ru and Al-Cu-Fe quasicrystals have been studied in the temperature range 4.2-300 K. Through measurements on samples annealed at various temperatures we found that ordering of the quasicrystalline phase has a strong influence on electrical properties. The largest temperature variations of the Hall coefficient were observed in highly ordered Al-Cu-Ru samples, which also show the highest resistivities. The temperature dependence of the Hall coefficient implies that there exists a change in the carrier density. The electrical transport below 30 K is consistent with weak-localization and electron-electron-interaction theories. Conversely, at temperatures above 30 K, the observations can be consistently understood by recognizing that the increase of carrier density with increasing temperature overcomes the decrease of mobility. The characteristics of transport above 30 K are qualitatively similar to those of normal semiconductors.