David Logan

Abstract:

The results of simulation studies of the localization and quantum-transport characteristics of a three-dimensional, off-diagonally disordered tight-binding model are reported. The disorder is characteristic of a hard-sphere fluid, with an exponential transfer-matrix element. The properties calculated include the density of states, the band-edge and mobility-edge trajectories, and the time dependence of the averaged probability, P»(t), that an excitation will be found at the site at which it was initially located. Localization of eigenstates is inferred from a criterion based on a cutoff in the inverse participation ratio, and an attempt is made to provide a reasoned estimate for the chosen cutoff via time-dependent studies of P»(t). Pronounced screening effects on the band-edge and mobility-edge trajectories are found and their physical origin is discussed. The consequences of varying the ratio of the hard-sphere diameter to the range of the exponential interaction are investigated. The results obtained for the hard-sphere fluid are contrasted with those for a randomly substituted lattice at the same density. © 1988 The American Physical Society.

Abstract:

The possible nature of the composition induced transition from superconductor to semiconductor in a system with obvious crystalline order - in association with equally obvious electronic disorder - is considered. Topics discussed include: structural parameters, superconductivity, IR spectra, the nature of superconductor-semiconductor transition, as well as percolation and disproportionation.

Abstract:

High resolution electron microscopy of very small (ca. 40 Å diameter) colloidal silver particles established their decahedral morphology.