Anderson localization of electron states in Al-Pd-Re quasicrystal

The influence of disorder on the critical electron states in a quasiperiodic lattice is a subject of intense research. In this work, we apply using hard x-ray photoelectron spectroscopy, density functional theory and resistivity  to establish occurrence of Anderson localization  in  a so-called "semiconducting" icosahedral quasicrystal Al-Pd-Re due to site disorder. Anderson localization is observed in  polygrain Al-Pd-Re, whose conductivity is an order of magnitude reduced  compared to the  single-grain  monocrystalline Al-Pd-Re. Curiously however, the spectral intensity of the localized electron states is enhanced  at the Fermi level  in the former. These extra states originate primarily from  Re 5d- Pd 4d hybridization, and are enhanced in polygrain i-Al-Pd-Re due to compositional difference, but are broadened because of disorder that brings about Anderson localization. This is established by the Mott variable range hopping behavior of conductivity, and the estimated localization length is 23 Å. In contrast,  the spectral shape of sg-Al-Pd-Re portrays a well-formed pseudogap, and exhibits excellent agreement with the  valence band calculated for ordered Al-Pd-Re, indicating absence of anderson localization.