Physical Phenomena in Superconducting Arrays, High-Tc Superconductors, and Composite Media

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9731511 Stroud Theoretical studies will be conducted in three areas of research. The first involves the study of the properties of superconducting arrays. The circumstances under which these arrays can be made to oscillate coherently will be studied by both numerical and analytical techniques. Additional calculations are planned to treat vortex motion, quantum effects, flux noise, a.c. magnetic susceptibility, classical magnetoresistance, and long-range interactions in such arrays, using a variety of theoretical techniques. The second area is a theoretical investigation of flux lattice melting and related phenomena, primarily in high temperature superconductors. A previously developed lowest-Landau level representation will be extended to treat flux lattice melting in the presence of disorder, and to study the behavior of the c-axis Josephson plasmon in the flux liquid state, both with and without disorder. Further calculations of flux lattice melting are planned in a uniformly frustrated XY model and a layered London model, both with and without pinning. As a speculative project, the possibility of extending these approaches to layered magnetic materials will be investigated. Finally, several aspects of the physics of classically inhomogeneous materials will be studied. The emphasis will be on the nonlinear optical response of such materials, and on the linear a.c. response of polycrystals of anisotropic materials (such as quasi-one-dimensional conducting polymers). It is also planned to examine the possibility of treating a disordered two-dimensional superconductor as a model system for chaotic propagation of classical electromagnetic waves. %%% Theoretical research will be conducted in three areas of research using numerical and analytical techniques. These three areas are the study of superconducting arrays; flux lattice melting; and classical inhomogeneous materials. The first two areas are ones which have received increased attention due t o their applicability to the high temperature superconductors. The third area is one of great interest in designing composite materials with unique (optical) properties. ***