OPTICAL CONDUCTIVITY OF INSULATING AL-BASED ALLOYS - COMPARISON OF QUASI-PERIODIC AND PERIODIC-SYSTEMS

We report on the optical conductivity of the structurally ordered icos ahedral quasicrystal Al70Pd20Re10 and the crystal Al2Ru obtained from the reflectance measured over a wide frequency range. Our results show that both the crystal and the quasicrystal are semiconductors and hav e quite similar band structure. The major difference between the two m aterials arises from the localization of the electronic states deep in side the band gap of the quasicrystal in spite of the metallic carrier density. We speculate that the quasiperiodic symmetry favors carrier localization.