Novel Studies of Vortex Matter and Peak Effect using In-Situ Neutron Scattering and AC Magnetization

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This individual investigator award is to a young professor for a study of vortex matter phases and phase transitions related to the peak effect in type-II superconductors, using in situ neutron scattering and ac magnetization measurements. In spite of the technological importance of type-II superconductors, the vortex matter phases are poorly understood. For many years, it was thought that a genuine order-disorder (melting) phase transition cannot occur in vortex matter systems due to the destructive effects of random pinning. Recently it was proposed that a topologically ordered vortex solid phase (Bragg glass) could exist in weakly disordered type-II superconductors. The melting (disordering) of the Bragg glass phase has been suggested as the origin of the well known but poorly understood peak effect anomaly seen in many type-II superconductors. There is preliminary experimental evidence suggesting that the peak effect is a genuine order-disorder phase transition in the superconducting vortex matter. This project will use in situ small angle neutron scattering to determine the vortex matter phase diagram in a classic type-II superconductor, Nb. The effects of disorder on the supercooling and superheating of vortex matter will be investigated. This project will also explore a possible application of neutron spin echo technique for studying the metastable vortex phases. These studies will establish a basic understanding of the magnetic properties of type-II superconductors. The graduate and undergraduate students participating in this project will have the opportunity to work at the Center for High-Resolution Neutron Scattering at the NIST and at the Institut Laue Langevin in Grenoble, France with researchers from around the world. This should prepare the students for future careers in academia, industry, or government.%%%Vortices in type-II superconductors form a condensed matter system of technological and scientific interests. Superconductors are of technological interest because they are able to carry high electrical currents without loss due to resistance. The current-carrying capability of a superconductor is determined by a subtle competition between the vortex-vortex interactions, the random pinning (vortex-pin interactions), and thermal fluctuations. In spite of the technological importance of type-II superconductors, the vortex matter phases are poorly understood. This individual investigator award is to a young professor who will study the physics of vortex matter using in situ neutron scattering and ac magnetization measurements. These studies will establish a basic understanding of the magnetic properties of type-II superconductors. The graduate and undergraduate students participating in this project will have the opportunity to work at the Center for High-Resolution Neutron Scattering at the NIST and at the Institut Laue Langevin in Grenoble, France with researchers from around the world. This should prepare the students for future careers in academia, industry, or government.***