Studies of Two-Dimensional Superconductors and Multilayers in Magnetic Fields

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9800663 Kapitulnik This experimental two investigator research project is concerned with detailed understanding of 2-D superconductivity. Four research topics are as follows: (a) The nature of the thermodynamic transition near Hc2, including the validity of the Lowest Landau Level approximation (b) The length scales associated with disorder, and, specifically, comparison of the length associated with crossover of the dynamics with the disorder length extracted from dc critical current measurements (c) The superconductor-insulator transition, with emphasis on possible quantum tunneling of vortices in the superconducting phase and possible effects of screening (from a groundplane) on the nature of the transition, and, (d) The effect of bias current on the vortex system in 2-D superconductors. A substantial portion of the work will involve multilayers of MoGe alloys. This system has proven to be an excellent model system in the investigation of 3-D to 2-D crossover effects in superconductivity. This highly interdisciplinary research will involve graduate student and postdoctoral researchers who will receive excellent training beneficial to their future careers in industry, government or academia. %%% This experimental two investigator basic research project focuses on the special features that occur as superconductor samples approach the limit of being two-dimensional. A two- dimensional sample is one that is so thin that no motion of carriers or electric current occurs in the direction perpendicular to the plane of the sample. The project will probe these properties in samples which are "superlattices" similar in nature to a deck of cards, where each card is a superconducting layer and a thin insulating layer is placed between each conducting layer. In this work the two types of layer will typically be alloys of Molybdenum and Germanium, which form an alloy syst em such that Ge-rich alloys are insulating and other alloy compositions can be metallic or superconducting. This system is chosen as a "model system" in which to carefully study effects that occur in materials of potential for applications, such as cuprate superconductors. The effects can be more reliably studied in the model system than in the cuprates. Thus the results of the basic study will lead to greater understanding of cuprate superconductivity, and may lead to new applications for these materials. This highly interdisciplinary research will involve graduate student and postdoctoral researchers who will receive excellent training beneficial to their future careers in industry, government or academia. ***