Are decagonal quasicrystals the Hume-Rothery phases?

Photoemission spectroscopy measurements in the photon energy range 40-100 eV have been used to make the first determinations of the valence bands of the high quality decagonal alloys Al₆₅Co₁₅Cu₂₀ and Al₇₀Co₁₅Ni₁₅. Within the energy resolution our results reveal that, contrary to the prediction of recent band-structure calculations and to the widespread qualitative interpretation of various electronic transport data, there is no pseudogap in the density of states at the Fermi level. This suggests that decagonal alloys differ significantly in their electronic structure from icosahedral alloys and that a Hume-Rothery mechanism does not play an important role in accounting for their stability and electronic transport properties.