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

We present a comprehensive series of results of electrical transport (elect rical conductivity, magnetoconductivity, Hall effect), thermal (specific he at), and optical (reflectivity) measurements in varying temperature ranges between 1.5 and 300 K on high-quality single-grain quasicrystals of icosahe dral Y-Mg-Zn. This data set is augmented by the specific-heat and optical-r eflectivity data obtained from a single-grain quasicrystal of icosahedral T b-Mg-Zn. For Y-Mg-Zn, both the electrical conductivity sigma(T) and magneto conductivity delta sigma(H) may be described by calculations considering qu antum interference effects. A detailed comparison of the weak-localization contributions to sigma(T) and delta sigma(H) with our experimental data pro vides estimates of the inelastic and spin-orbit relaxation rates. The inela stic relaxation rate is found to be proportional to T-3. The dominant contr ibutions to the optical conductivity sigma(1)(omega) spectrum, obtained fro m the reflectivity R(omega) data in the frequency range between 16 and 9.7 X 10(4) cm(-1), are a strong Drude feature at low frequencies and a promine nt absorption signal centered at approximately 6 X 10(3) cm(-1). A comparis on of the spectral weight of the Drude contribution to sigma(1)(omega) with the magnitude of the linear-in-ir term gamma T of the low-temperature spec ific heat C-p(T) yields the itinerant charge-carrier density n(i) = 7.62 X 10(21) cm(-3) or 0.13 charge carriers per atom. The low ni value is corrobo rated by the results of the Hall effect measurements. For Tb-Mg-Zn, the opt ical conductivity sigma(1)(omega) spectrum reveals features similar to thos e of Y-Mg-Zn. The low-temperature specific heat C-P(T) of Tb-Mg-Zn is stron gly influenced by a spin-glass-type freezing of Tb moments and by crystal-e lectric-field effects.