Electronic density of states and metastability of icosahedral Au-Al-Yb quasicrystal

The recently discovered icosahedral quasicrystal (i-QC) in the ternary Au-Al-Yb system at the composition Au51Al34Yb15 is formed only in as-cast alloys and is metastable with decomposition to other crystalline phases upon annealing at 700 °C. Measuring the electronic transport coefficients (electrical resistivity, thermoelectric power, Hall coefficient), magnetic susceptibility and specific heat, we addressed the question of metastability of the i-Au-Al-Yb quasicrystalline phase by reconstructing the shape of the electronic density of states (DOS) in the vicinity of Fermi level ɛF with the aim to find out whether there exists a pseudogap in the DOS that could contribute to electronic stabilization of the icosahedral phase. The results have revealed that the DOS in the vicinity of ɛF exhibits a pronounced valley on a 100 meV energy scale with a sharp feature on a 10 meV scale, both being centered almost exactly at ɛF. This pseudogap is apparently not wide enough to ensure sufficient electronic energy gain of the order of a few 10 kJ/mol needed for the electronic stabilization of the icosahedral phase. A possible origin of metastability of the i-Au-Al-Yb quasicrystal and thermodynamic stability of its 1/1 cubic approximant of very similar composition is discussed. The sharp feature in the DOS at ɛF is proposed to originate from indirect interaction between localized Yb f-moments due to overlap of their polarization clouds in the presence of hybridization of the f and s states, which leads to a sharp resonance peak.