Compositional Dependence of Electronic Specific Heat in AlCuCo Decagonal Quasicrystals: Evidence for the Hume--Rothery Mechanism of Phase Formation

There is no consensus whether the electron density of states of decagonal quasicrystals has a pseudogap at the Fermi energy similar to that of the icosahedron phase. We answer this question by measuring the electronic specific heat coefficient of AlCuCo decagonal single-quasicrystals over a wide range of composition. While the average valence electron number per atom, e/a, for all the resultant samples changes only within 1.5%, from ～1.92 to less than 1.95. The specific heat coefficient decreases by 15% with the increasing e/a. The large change and the negative slope give strong evidence for Hume--Rothery mechanism of the decagonal phase.