Session CC - Condensed Matter I.
MIXED session, Friday morning, November 15
Henry Oliver E, Holiday Inn
The electronic properties of quasicrystals and their crystalline approximants have been studied by ^27Al nuclear magnetic resonance. An anomalous temperature dependence of the spin-lattice relaxation rate (T_1^-1), T_1^-1 \sim T^2, was observed in a broad temperature range in i-AlCuFe, R-AlCuFe, i-AlCuRu, i-AlPdRe, and \alpha-AlMnSi. This temperature dependence can be explained by the presence of a pseudogap described by g(E) \sim |E-E_F|^1/2. This type of density-of-state was predicted by a recent theoretical calculation(C. Janot et. al., Phys. Rev. Lett. 72, 1674(1994)) and also was indicated by a recent photonemission measurement (X. Wu et. al., Phys. Rev. Lett. 75, 4540(1995)) in i-AlPdMn. Our NMR results gave the first experimental evidence that this special electronic density-of-state is a common feature in quasicrystals. For all these samples, reasonable width of the pseudogap has been obtained from the temperature dependence of the spin-lattice relaxation rate. A weak temperature dependence of the Knight shift K \sim T^1/2, as a result of g(E) \sim |E-E_F|^1/2 is also consistent with our ^27Al measurements.