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

这个个人研究奖是给一位年轻的教授，他使用原位中子散射和交流磁化测量研究了与II型超导体峰值效应相关的涡旋物质相和相变。尽管第二类超导体在技术上很重要，但人们对涡旋物质相的了解却很少。多年来，人们一直认为，由于随机钉扎的破坏性影响，真正的有序-无序（熔化）相变不可能发生在涡旋物质系统中。最近有人提出，拓扑有序的涡旋固相（布拉格玻璃）可以存在于弱无序的II型超导体。布拉格玻璃相的熔化（无序化）被认为是许多II型超导体中众所周知但知之甚少的峰值效应异常的起源。有初步的实验证据表明，峰值效应是一个真正的有序无序相变的超导涡旋物质。这个项目将使用原位小角中子散射来确定经典的II型超导体Nb中的涡旋物质相图。无序对涡旋物质的过冷和过热的影响将被研究。本计画亦将探讨中子自旋回波技术在研究亚稳涡旋相的可能应用。这些研究将建立对第二类超导体的磁性的基本理解。参与该项目的研究生和本科生将有机会在NIST的高分辨率中子散射中心和法国格勒诺布尔的劳厄朗之万研究所与来自世界各地的研究人员一起工作。这应该为学生将来在学术界，工业界或政府部门的职业生涯做好准备。%第二类超导体中的涡旋形成了一个具有科学和技术意义的凝聚态系统。超导体是技术上感兴趣的，因为它们能够携带高电流而不会由于电阻而损失。 超导体的载流能力由涡旋-涡旋相互作用、随机钉扎（涡旋-钉扎相互作用）和热涨落之间的微妙竞争决定。尽管第二类超导体在技术上很重要，但人们对涡旋物质相的了解却很少。这个个人研究奖是给一位年轻的教授，他将使用原位中子散射和交流磁化测量来研究涡旋物质的物理学。这些研究将建立对第二类超导体的磁性的基本理解。参与该项目的研究生和本科生将有机会在NIST的高分辨率中子散射中心和法国格勒诺布尔的劳厄朗之万研究所与来自世界各地的研究人员一起工作。这应该为学生未来在学术界，工业界或政府的职业生涯做好准备。

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.***