Optical conductivity of the stable icosahedral quasicrystalAl63.5Cu24.5

Abstract

The optical properties of the stable icosahedral quasicrystal Al63.5Cu24.5Fe12 have been measured from 40 to 25 000 cm -1 at 300 K and at 80 K. 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 -1 ; its position and strength suggest that it arises from a direct excitation of phonons.

Two-Level Electron Excitations and Distinctive Physical Properties of Al-Cu-Fe Quasicrystals

“…The optical conductivity σ(ω) of Al 63 Cu 25 Fe 12 at room temperature is shown in Figure 7 in accordance with experimental data [39]. It presents an intense, broad and practically featureless (except for maximum) band occupying virtually the all range of frequencies from 40 up to 25,000 cm −1 .…”

“…The result is shown by dash-dotted line on Figure 7a. Intriguing was the [39]). The dash-dotted line (1400) is a fit with the Lorentzian peak according to Equation (8).…”

Interactions in Quasicrystals

“…For example, in AlCuF e 3 and AlCuRu 4 , a finite conductivity at zero temperature is expected whereas recent results 5 seem to confirm a Mott's variable range hopping mechanism (σ(T ) ∼ exp −(T 0 /T ) 1/4 ) for i − AlP dRe icosahedral phase down to 20 mK. The optical conductivity is also unusual since there is no Drude Peak for icosahedral quasicrystals 6,7 . From a theoretical point of view, the case of independent electrons in one-dimensional (1D) systems has been deeply investigated for different quasiperiodic structures (Harper model, Fibonacci chain,..) 8,9 , giving rise to singular continuous spectra with an infinite number of gaps.…”

“…In contrast, given the complexity of the Fourier spectrum, one can expect the long distance physics of the interacting system to depend on the position of the Fermi level. Indeed, the flow equations (6) show that the behaviour of G is strongly sensitive to the position of the window in the spectrum. For a given maximum renormalization length scale l max ,corresponding to accessible physical range, two different cases must be distinguished.…”

Recubrimientos autolubricantes cuasicristalinos tipo composite depositados mediante proyección térmica para aplicaciones espaciales y de alta temperatura

“…Los cuasicristales presentan características muy atractivas: alta dureza 103,104 , baja fricción 105 , resistencia a la oxidación y a la corrosión 106,107 , baja conductividad eléctrica y térmica 108,109 , y propiedades ópticas sorprendentes 110 .…”