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

这一个人研究人员奖支持一个解决与第二类超导体涡旋状态有关的基本问题的项目。第二类超导体具有广泛的科学和技术重要性，其物理性质受涡旋态的基本物理控制。最近在弱钉扎晶体Nb上的中子散射实验在众所周知的峰值效应反常处发现了Bragg玻璃熔化(无序)转变，并在Bragg玻璃相界上发现了一个多临界点，这表明Bragg玻璃相的形成既可以是Abrikosov预测的从正常态直接到平均场的转变，也可以是根据Bragg玻璃理论从无序涡旋液体(或玻璃)的一级冻结转变。提出的方案是利用小角中子散射和其他补充技术来测试在Nb中发现的新的涡旋相图是否适用于其他重要的II类超导体，以及峰值效应是否与涡旋物质中的其他类型的相变有关。所提出的工作将导致对第二类超导体的基本性质的新的见解，并对具有随机钉扎的凝聚态系统中的相和相变有更深刻的理解。研究生和本科生将学习最先进的中子散射技术，获得广泛的热力学和超声波测量方面的材料研究经验，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。第二类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。混合态由超导区和含有磁场的非超导区组成。这些后一区域被称为漩涡。第二类超导体具有广泛的科学和技术重要性，其物理性质受涡旋态的基本物理控制。这一个人研究人员奖支持一个解决涡旋状态基本问题的项目。最近在著名的第二类材料Nb上进行的中子散射实验发现了涡旋态的熔融型相变。这导致了新发现的相图，即当温度和/或磁场发生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Nb中的涡旋相图是否适用于其他重要的第二类超导体。这项拟议的工作将使人们对第二类超导体的基本性质有了新的认识，并对超导材料中的相和相变有了更深刻的理解。研究生和本科生将学习最先进的中子散射技术，获得广泛的热力学和超声波测量方面的材料研究经验，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.