RUI: Core Size Effects on Flux-Flow Resistivity: Collaborative Project to Launch a Program Exploring Flux Dynamics in Weak-Pinning Systems

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Abstract, non-technical:This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The US is in dire need to modernize its aging electric power grid, a fact underscored recently by the widespread power outage in the Northeast in August 2003. Also, the conducting materials used in the present grid release waste heat to the environment, worth billions of dollars annually in electricity that never reaches its users. This is due to the dissipative resistance in conventional conductors. Superconductors, on the other hand, conduct electricity with zero dissipation. Thus, scientists and engineers throughout the US and around the world are actively developing superconducting lines for grid modernization, which has made the understanding of the electromagnetic properties of superconducting compounds a major research priority. Of these, one critical set of mechanisms is in how magnetic fields penetrate the interior of technologically relevant superconductors under various conditions. Such penetration occurs in the form of vortices ? discrete quanta of magnetic flux which also interact with each other. The motion of these vortices greatly affects the current-carrying capability of superconductors; thus the nature of vortex dynamics has been widely investigated. The interest in the present project is in how the internal structure or cores of these vortices affect their free motion ? something rarely studied, since free motion is achieved under technically challenging conditions achieved only by this group and few others. The project is also designed to be run by undergraduate students, thus preparing them for careers in science.Abstract, technical:This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The dynamics of magnetic flux quanta (also known as vortices, flux lines, or fluxons) ? by which an external magnetic field begins to penetrate the interior of technologically relevant type II superconductors ? continues to be a research priority in understanding and applying these materials, most notably high-temperature cuprates. A particular aspect being explored by various groups is the nature of the non-superconducting cores of these flux quanta, which is still not completely understood but is already known to affect the interactions between flux quanta and thus the nature of phase transitions in ?flux matter? under various conditions. One rarely studied aspect of flux cores which this project is uniquely poised to explore is the effect of cores particularly on the field dependence of flux flow resistivity, which is the DC-driven dissipation associated with the free flux flow (FFF) phase, a highly ordered dynamic phase wherein the elasticity of the flux matter overcomes disorder-inducing pinning and thermal fluctuations. Complementing the DC transport measurements are magnetization, heat capacity, and NMR on the same samples ? via present and future collaborations. All this is to be performed on already available, high-quality, crystals of at least four different materials to explore compound-dependent subtleties. The ultimate goal is to provide a uniquely comprehensive view into the nature of the flux core. The project is also designed to provide research experience to physics undergraduates in preparation for graduate studies and beyond; therefore students are to be actively involved.