Low-temperature transport, thermal, and optical properties of single-grain quasicrystals of icosahedral phases in the Y-Mg-Zn and Tb-Mg-Zn alloy systems

We present a comprehensive series of results of electrical transport (electrical conductivity, magnetoconductivity, Hall effect), thermal (specific heat), and optical (reflectivity) measurements in varying temperature ranges between 1.5 and 300 K on high-quality single-grain quasicrystals of icosahedral Y-Mg-Zn. This data set is augmented by the specific-heat and optical-reflectivity data obtained from a single-grain quasicrystal of icosahedral Tb-Mg-Zn. For Y-Mg-Zn, both the electrical conductivity $\sigma \mathrm{}\left(T\right)\mathrm{}$ and magnetoconductivity $\delta \sigma \mathrm{}\left(H\right)\mathrm{}$ may be described by calculations considering quantum interference effects. A detailed comparison of the weak-localization contributions to $\sigma \mathrm{}\left(T\right)\mathrm{}$ and $\delta \sigma \mathrm{}\left(H\right)\mathrm{}$ with our experimental data provides estimates of the inelastic and spin-orbit relaxation rates. The inelastic relaxation rate is found to be proportional to $T^3.$ The dominant contributions to the optical conductivity ${\sigma }_1\left(\omega \right)$ spectrum, obtained from the reflectivity $R\left(\omega \right)$ data in the frequency range between 16 and $9.7\times {10}^4\hspace{0.5em}{\mathrm{cm}}^{-1},$ are a strong Drude feature at low frequencies and a prominent absorption signal centered at approximately $6\times {10}^3\hspace{0.5em}{\mathrm{cm}}^{-1}.$ A comparison of the spectral weight of the Drude contribution to ${\sigma }_1\left(\omega \right)$ with the magnitude of the linear-in-$T$ term $\gamma T$ of the low-temperature specific heat $C_p\mathrm{}\left(T\right)\mathrm{}$ yields the itinerant charge-carrier density $n_{\mathrm{i}}=7.62\mathrm{}\times {10}^{21}\hspace{0.5em}{\mathrm{cm}}^{-3}$ or 0.13 charge carriers per atom. The low $n_{\mathrm{i}}$ value is corroborated by the results of the Hall effect measurements. For Tb-Mg-Zn, the optical conductivity ${\sigma }_1\left(\omega \right)$ spectrum reveals features similar to those of Y-Mg-Zn. The low-temperature specific heat $C_p\mathrm{}\left(T\right)\mathrm{}$ of Tb-Mg-Zn is strongly influenced by a spin-glass-type freezing of Tb moments and by crystal-electric-field effects.