Showing papers by "Yue Wu published in 1997"

Sharp Feature in the Pseudogap of Quasicrystals Detected by NMR

Abstract: The {sup 27}Al and {sup 63}Cu spin-lattice relaxation rates were found to contain a large T{sup 2} term over a wide temperature range below 400K in several thermodynamically stable quasicrystalline alloys, including i -AlCuRu, i -AlPdRe, i -AlCuFe, and the crystalline approximant phase {alpha}-AlMnSi. The relaxation mechanism is proven to be electronic in origin. Such nonlinear temperature dependence is shown to be a clear signature of sharp features in the density of states at the Fermi level. The estimated width of this sharp feature is on the order of 20meV. {copyright} {ital 1997} {ital The American Physical Society}

An NMR Investigation of H Cluster Configurations in A-SI:H

Abstract: In this work the characteristics of hydrogen clusters in hot filament assisted CVD and conventional glow discharge a-Si:H films are discussed. Computer simulations of the observed free-induction decays of the 1H NMR signals indicate that the distribution of the nearest-neighbor distances between H atoms in the H clusters is quite narrow in hot filament assisted CVD a-Si:H whereas the distribution is larger in glow discharge a-Si:H. This is clear evidence of improved structural order in hot filament assisted CVD a-Si:H. The relaxed hydrogenated divacancy and multi-vacancy models reproduce the main features of the observed free-induction decay in hot-wire a-Si:H very well. Computer simulations of the multiple-quantum NMR spectra indicate that a relaxed hydrogenated divacancy configuration leads to good agreement with experimental observations in device quality glow discharge a-Si:H. Results of simulations based on other H cluster configurations are also discussed. These results provide restrictions on the possible models for H clusters in a-Si:H.