SGER: In-Situ Measurements of Small Angle Neutron Scattering and AC Magnetic Susceptibility of Vortex Matter

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0075838LingThis is a Small Grant for Exploratory Research (SGER) to a young faculty member at Brown University. He will study vortex phases in the regime where the random potential caused by defects in the material competes with vortex-vortex interactions and thermal fluctuations giving rise to the "peak effect" in type-II superconductors. The vortex physics in this regime will be studied in a single crystal of Nb using a coil wound directly on the sample to measure the vortex dynamics and simultaneously using Small Angle Neutron Scattering (SANS) to measure the neutron diffraction pattern of the vortex array. This experiment is highly exploratory since the neutron diffraction signal from a vortex array is very weak in the peak effect regime. If successful, this project will generate experimental results that will reveal the direct correlation between the microscopic properties of the vortex lattice and the macroscopic properties of a type-II superconductor in a magnetic field. The question of vortex pinning-depinning is one of technological importance and thus this research could have a high payoff. A graduate student will participate in this research, thereby gaining the experience of working at a National Facility (the Center for High-Resolution Neutron Scattering at NIST) as well as working on a high-risk, high payoff project. This should prepare the student for future work in academia, industry, or government.%%%The capability to carry an electric current without dissipation makes superconductors useful in many applications such as MRI magnets, power transmission, etc. Most technologically useful superconducting materials allow a strong magnetic field to penetrate into the material to form quantized magnetic vortices. In an ideal, defect-free type-II superconductor these vortex lines will move and cause dissipation under the driving force of a current. Fortunately, imperfections, defects, and impurities, in the atomic lattice can pin the vortex lines, allowing a superconducting wire to carry a large lossless current. Therefore a good understanding of the pining of the vortex lattice by random impurities is beneficial to many applications. This Small Grant for Exploratory Research (SGER) will fund a project that will use a neutron beam to study the microscopic structure of the vortex lattice that gives rise to what is known as the anomalous peak effect. This effect allows a superconductor to carry more current at a higher magnetic field and temperature. If successful this project will reveal the direct correlation between the microscopic structure of the vortex lattice and the macroscopic properties of a type-II superconductor in a magnetic field, and thus help scientists make better superconductors. The graduate student participating in this project will have the opportunity to work at a National Facility (the Center for High-Resolution Neutron Scattering at NIST) with researches from around the country. This should prepare the student for future work in academia, industry, or government.***