Investigation of Vortex Matter Phase Transitions in Type-II Superconductors using Small Angle Neutron Scattering and Complementary Techniques

这个个人研究者奖支持一个项目，解决有关第二类超导体的涡旋状态的基本问题。 第二类超导体具有广泛的科学和技术重要性，它们的物理性质由涡旋态的基本物理控制。 最近对弱钉扎晶体Nb的中子散射实验发现了布拉格玻璃熔化在著名的峰值效应异常处的（无序）转变，以及布拉格玻璃相边界上的多临界点，表明布拉格玻璃相的形成可以是如Abrikosov预测的直接从正常态的平均场转变，或者如布拉格玻璃理论所设想的从无序涡旋液体（或玻璃）的一级凝固转变。 拟议的计划是利用小角中子散射和其他补充技术来测试在Nb中发现的新涡旋相图是否适用于其他重要的II型超导体，以及峰值效应是否与涡旋物质中其他类型的相变有关。拟议的工作将导致对II型超导体的基本性质的新见解，以及对具有随机钉扎的凝聚态系统中的相和相变的坚定理解。 研究生和本科生将学习最先进的中子散射技术，在热力学和超声测量方面获得广泛的材料研究经验，并参与超导的前沿研究。因此，他们将为未来在学术界，工业界或政府部门的职业生涯做好准备。II型超导体是那些在一定温度和磁场条件下具有混合状态的超导体。 混合态由超导区域和含有磁场的非超导区域组成。 后面这些区域被称为涡流。 第二类超导体具有广泛的科学和技术重要性，它们的物理性质由涡旋态的基本物理控制。 这项个人研究奖支持一个解决涡旋状态基本问题的项目。 最近的中子散射实验上著名的第二类材料铌导致发现的熔融型相变的涡旋状态。 这导致了一个新发现的相图，或当温度和/或磁场变化时涡旋状态的行为。该项目将使用小角中子散射和其他补充技术来测试铌中的涡旋相图是否适用于其他重要的II型超导体。拟议的工作将导致对II型超导体的基本性质的新见解，以及对超导材料中的相和相变的坚定理解。 研究生和本科生将学习最先进的中子散射技术，在热力学和超声测量方面获得广泛的材料研究经验，并参与超导的前沿研究。因此，他们将为未来在学术界，工业界或政府的职业生涯做好准备。

This individual investigator award supports a project addressing the fundamental issues concerning the vortex state of type-II superconductors. Type-II superconductors are of broad scientific and technological importance, and their physical properties are controlled by the basic physics of the vortex state. Recent neutron scattering experiments on weak-pinning crystalline Nb have led to the discovery of a Bragg-glass melting (disordering) transition at the well-known peak-effect anomaly, and a multicritical point on the Bragg-glass phase boundary, suggesting that the formation of the Bragg glass phase can be either a mean-field transition directly from the normal state as predicted by Abrikosov, or a first-order freezing transition from a disordered vortex liquid (or glass) as envisioned by the Bragg glass theory. The proposed program is to use small angle neutron scattering and other complementary techniques to test whether the new vortex phase diagram discovered in Nb is applicable to other important type-II superconductors, and whether the peak effect is related to other types of phase transitions in vortex matter. The proposed work will lead to new insights into the fundamental properties of type-II superconductors, and a firm understanding of the phases and phase transitions in condensed matter systems with random pinning. The graduate and undergraduate students will learn state-of-the-art neutron scattering techniques, acquire a wide range of materials research experiences in thermodynamic and ultrasonic measurements, and participate in the frontier research of superconductivity. Thus, they will be prepared for future careers in academia, industry, or government.Type-II superconductors are those that, under certain temperature and magnetic field conditions, have a mixed state. The mixed state consists of superconducting regions as well as non-superconducting regions containing a magnetic field. These latter regions are known as vortices. Type-II superconductors are of broad scientific and technological importance, and their physical properties are controlled by the basic physics of the vortex state. This individual investigator award supports a project addressing the fundamental issues of the vortex state. Recent neutron scattering experiments on the well-known type-II material niobium led to the discovery of a melting-type phase transition in the vortex state. This led to a newly discovered phase diagram, or behavior of the vortex state when then the temperature and/or the magnetic field are varied. The project will use small angle neutron scattering and other complementary techniques to test whether the vortex phase diagram in niobium is applicable to other important type-II superconductors. The proposed work will lead to new insights into the fundamental properties of type-II superconductors, and a firm understanding of the phases and phase transitions in superconducting materials. The graduate and undergraduate students will learn state-of-the-art neutron scattering techniques, acquire a wide range of materials research experiences in thermodynamic and ultrasonic measurements, and participate in the frontier research of superconductivity. Thus, they will be prepared for future careers in academia, industry, or government.