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

Recent theoretical works have predicted that quasicrystals (QCs) have conspicuous fine electronic structures near the Fermi level (EF); the density of states (DOS) consists of sharp peaks and deep valleys with several lOmeV intervals, which is often called spiky structures. These fine electronic structures are believed to explain the extremely high resistivity of QCs. However, no experiment of observing the fine structures has succeeded for more than ten years. Wehave investigated the DOS around EF on icosahedral (i-)AlCuFe, i-AlPdMn, and decagonal (d-)AlCuCo quasicrystals by break junction tunneling spectroscopy at 4.2K and have observed clear peaks of 3.3 ~ 125mV width near EF. Each peak can be expressed by the probability distribution of the narrow energy gaps that are similar to BCS gaps. This is the first direct experimental result that confirms the predicted spiky structures existing in the vicinity of EF.