Evidence of the Fine Pseudogap at the Fermi Level in Al-based Quasicrystals

Theoretical studies have predicted that quasicrystals (QCs) have conspicuously fine electronic structures near the Fermi level ( E F ); the density of states (DOS) consists of sharp peaks and deep valleys with several 10 meV intervals. These fine electronic structures are believed to explain the unusual sensitivity of the electrical conductivity to slight changes in the chemical composition of QCs. We have investigated the DOS around the E F on single grains of icosahedral ( i -)AlCuFe, i -AlPdMn, and decagonal ( d -)AlCuCo QCs by break-junction tunneling spectroscopy at 4.2 K. Well-defined and reproducible pseudogaps at the E F are observed for these alloys. This is a direct experimental result that confirms the fine electronic structure existing in the vicinity of the E F .