Band-structure gap and electron transport in metallic quasicrystals and crystals

Studies of icosahedral quasicrystals have revealed a conductivity pseudogap much narrower than the density-of-states pseudogap, resulting in a rapid suppression of electron diffusivity inside the latter. In contrast, measurements of the new metallic compounds ${\mathrm{Al}}_2$Ru show the formation of a semiconductinglike gap with localized gap states. The imminence of Anderson localized and absence of a real gap in quasicrystals are compared with current calculations of electronic properties on metallic quasiperiodic, as well as periodic, systems.