Electrical, magneto-, and optical conductivity of quasicrystals in the Al-Re-Pd system

Measurements of the electrical conductivity σ(T) and magnetoconductivity Δσ(H) of icosahedral ${\mathrm{Al}}_{70}$ ${\mathrm{Re}}_{10}$ ${\mathrm{Pd}}_{20}$ and ${\mathrm{Al}}_{70}$ ${\mathrm{Re}}_{8.6}$ ${\mathrm{Pd}}_{21.4}$ quasicrystals at low temperatures and in high magnetic fields H are reported. Below 0.2nK, σ of ${\mathrm{Al}}_{70}$ ${\mathrm{Re}}_{10}$ ${\mathrm{Pd}}_{20}$ varies as σ(T)=${\mathrm{\sigma }}_0$+${\mathrm{aT}}^{1\mathrm{/}2}$ with ${\mathrm{\sigma }}_0$=30 ${\mathrm{\Omega }}^{\mathrm{-}1}$ ${\mathrm{cm}}^{\mathrm{-}1}$ and a<0. The conductivity decreases with increasing magnetic field. For ${\mathrm{Al}}_{70}$ ${\mathrm{Re}}_{8.6}$ ${\mathrm{Pd}}_{21.4}$ σ(T) decreases with decreasing T and saturates at the level ${\mathrm{\sigma }}_0$=1.7n${\mathrm{\Omega }}^{\mathrm{-}1}$ ${\mathrm{cm}}^{\mathrm{-}1}$ below 0.1nK. In magnetic fields up to 40 kOe, Δσ(H) is negative below 1 K and σ(T,H) remains temperature-independent at the lowest temperatures. The optical conductivity σ(ω) is obtained from reflectivity data in the frequency range between 15 and ${10}^5$ ${\mathrm{cm}}^{\mathrm{-}1}$. The main contributions to σ(ω) are a broad absorption signal centered at about 0.1neV and a sizable peak with its maximum at 2.6neV.