Low-temperature thermal conductivity of icosahedral ${\mathrm{Al}}_{70}$${\mathrm{Mn}}_9$${\mathrm{Pd}}_{21}$

We report measurements of the thermal conductivity λ(T) of icosahedral ${\mathrm{Al}}_{70}$ ${\mathrm{Mn}}_9$ ${\mathrm{Pd}}_{21}$ in the temperature range 0.06–110 K. The quasilattice thermal conductivity ${\lambda }_{\mathrm{ph}}$ increases monotonically with T in the temperature range between 0.06 and 25 K and above 55 K. A plateau is observed for ${\lambda }_{\mathrm{ph}}$(T) between 25 and 55 K, i.e., at substantially higher temperatures than in amorphous solids. Moreover, the thermal conductivity of icosahedral ${\mathrm{Al}}_{70}$ ${\mathrm{Mn}}_9$ ${\mathrm{Pd}}_{21}$ in the λ plateau region is substantially higher than that of insulating and metallic glasses. At lower temperatures, between 0.35 and 1.6 K, ${\lambda }_{\mathrm{ph}}$ varies as ${\mathit{T}}^{2.06}$. This ${\lambda }_{\mathrm{ph}}$(T) variation is compatible with a scattering of phonons by tunneling states. Below 0.35 K the thermal conductivity decreases with increasing slope suggestive of a crossover to a regime of excessive phonon scattering characterized by a temperature-independent mean free path.