David Logan

Abstract:

We discuss an Onsager reaction field approach to the paramagnetic phase of a spatially anisotropic Heisenberg model, with nearest-neighbor in-plane (J) and interplane (J) exchange couplings. The theory is physically transparent and, together with the use of suitable asymptotic approximations, provides a simple, consistent description of the crossover from effective two- to three-dimensional behavior, and captures well both the pure d=2 (=0) and d=3 (J=J) dimensional limits. Application to La2CuO4 is briefly considered. © 1995 The American Physical Society.

Abstract:

We consider the electronic structure of "simple" liquid charge-transfer alloys Cy[CA]1-y, in which the effects of disorder, electron interactions, and their interplay are argued to underly observed experimental behaviour. The primary source of disorder arises from the random Coulomb fields due to both ionic species, and Monte Carlo simulations of the primitive model are undertaken to ascertain the probability densities of local Madelung fields. The electronic structure of the system in the C-rich domain (y > 0) is then considered via numerical study, at a mean-field level, of a spatially and Coulombically disordered Anderson-Hubbard model for the C species conduction band. The results are in accord both with the experimental behaviour of liquid Csy[CsAu]1-y and with recent related theoretical work. © 1994 American Chemical Society.

Abstract:

The presence of disorder, reflecting a range of local environments may lead to local moment formation on an inhomogeneous scale; the essential element of the theory is a self-consistent description of local charges and magnetic moments on sites of different site energies, in , arising from the occurrence of site disorder. The authors consider self-consistently determined local and total pseudoparticle spectra, in -dependent site occupation probabilities, and a measure of the Fermi-level charge distribution over the sites. Particular attention is given to the evolution of the interplay between disorder and interactions as the band filling fraction, y, is increased from y approximately=0 through to the half-filled limit, y=1.