Transport Properties of the Au-Al-Yb Quasicrystal and Approximant under Hydrostatic Pressure

The mixed-valence Au-Al-Yb quasicrystal exhibits unusual quantum criticality. Its crystalline approximant behaves like a conventional heavy fermion metal. Due to these novel features, they have attracted much attention recently. To examine the sample dependence of this new type of materials, we have prepared several samples and measured the electrical resistivity both at ambient and high pressures as well as the magnetic susceptibility at ambient pressure. The residual resistivity ratio of the quasicrystals is almost sample independent while the power law exponent n of the electrical resistivity varies from sample to sample. The effective magnetic moment $p_{eff}$ of the quasicrystals is also sample dependent, ranging from about 3.4 to 3.9 $μ_{B}$/Yb, and these values are all smaller than the free $Yb^{3+}$ ion value, confirming the mixed-valence nature. Although the magnitude of n and $p_{eff}$ is sample-dependent, the principal feature of the mixed-valence is confirmed in all the samples studied thus far. A combination of these results indicates correlation between n and $p_{eff}$, suggesting that the 4f electrons may contribute to a scattering mechanism of the conduction electrons. External pressure increases the magnitude of the electrical resistivity and decreases the index n of both the quasicrystal and the approximant. Up to the highest pressure measured in the present study no experimental evidence for a phase transition was found