OPTICAL CONDUCTIVITY OF ICOSAHEDRAL QUASI-CRYSTALS

It is argued that the optical conductivity of face-centred icosahedral (FCI) quasi-crystals is dominated by band-structure effects. No mechanism peculiar to quasi-periodicity is necessary to explain experiment which is accounted for by semi-phenomenological perturbation theory. What makes FCI quasi-crystals different from conventional metallic alloys is the high multiplicity (namely, 42) of their reciprocal lattice vectors, which allows a better match between the Fermi sphere and the corresponding set of Bragg planes (the 'quasi-Brillouin zone'). This effect is also responsible for a strong reduction in the DC conductivity through a substantial optical mass increase, rather than anomalously strong scattering localization. The low DC conductivity, in tum, means that the weak Drude part of the AC conductivity is overwhelmed by stronger interband absorption, resulting in a suppression of the Drude peak. Otherwise, however, the interband absorption peak in an FCI quasicrystal is not significantly different from those in conventional metals.