Optical conductivity of the stable icosahedral quasicrystal Al63.5Cu24.5Fe12

The optical properties of the stable icosahedral quasicrystal Al63.5Cu24.5Fe12 have been measured from 40-25 000 cm exp --1 at 300 and at 80K. Unlike metallic glasses with a Drude spectrum with strong elastic scattering by disorder, or semiconductors with a conductivity gap, the optical conductivity of this quasicrystal is distinctive: starting from the very low dc value, it increases linearly with frequency well into the near infrared. A prominent peak in the conductivity is observed at 245 cm exp --1 ; its position and strength suggest that it arises from a direct excitation of phonons.