Semiconductivity in aluminum–transition-metal quasicrystalline alloys induced by ordering in six dimensions

¹ Institut für Materialphysik and Center for Computational Materials Science Universität Wien - Sensengasse 8/12, A-1090 Wien, Austria
² Institute of Physics, Slovak Academy of Sciences Dúbravská cesta 9, SK-84228 Bratislava, Slovak Republic

Received: 23 January 2003
Accepted: 2 May 2003

Abstract

We report on a class of icosahedral aluminum–transition-metal (-TM) alloys with true semiconducting behavior. The existence of a semiconducting gap is found to depend critically on a particular kind of -TM ordering defined by a simple rule in the 6-dimensional superspace. Any deviation from this 6D order leads to the formation of strongly localized defect states in the gap. We show that by a judicious selection of transition metals to be alloyed with , we can find alloys with a semiconducting gap at the Fermi level for a hierarchy of approximants to a quasicrystal. As the electron/atom ratio placing the Fermi level into the gap is slightly different for each approximant, this suggests that the gap persists also in the quasiperiodic limit. Icosahedral -- turns out to be a semiconductor with a band gap filled by the localized states.