Materials Studies and Superconductivity of Uranium Platinum 3

铀铂3的材料研究和超导性

• 批准号: 9705473
• 负责人: William Halperin
• 金额: $ 54万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-12-01 至 2001-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9705473&HistoricalAwards=false
• 关键词: Materials; Studies; Superconductivity; Uranium; Platinum

9705473 Halperin The Ambitious goal of this program is to understanding the mechanism for superconductivity in heavy fermion compounds. The first step is to identify the symmetry of the order parameter and we focus first on Upt3, which is arguably the prototype unconventional heavy fermion superconductor. In order to determine the pairing state in Upt3 we propose to make single crystals with a range of impurities and measure the impurity dependence of the physical properties, including the thermal conductivity, specific heat and the phase diagram. In order to identify the spin structure of the pairing state, we will measure NMR knight shifts and the upper critical fields and compare with calculations that are sensitive to surface scattering and strong spin-orbit interactions. We will perform measurements of magnetization and magnetoresistance and, with our collaborators at other institutions, we will investigate further the magnetic phase diagram using neutron and magnetic X-ray scattering. We will compare these results with calculations of impurity and defect scattering on the physical properties for the principal candidate ground states. The low-temperature transport coefficients, eg. thermal conductivity, are important because they reflect the low enrgy excitations associated with the nodes of the gap. We believe that transport measurements on high quality single crystals, such as we are able to grow, will be decisive in resolving the orbital symmetry of the pairing state in heavy fermion superconductors, e.g. Upt3. %%% It is proposed to solve key problems in heavy fermion superconductivity with initial focus on the important compound Upt3. The results of this research will have impact on understanding of superconductivity in other correlated fermion superconductors, notably high temperature superconductors. That superconductivity in Up t3 is unconventional, is evident in its complex phase diagram and the power laws that are exhibited in the temperature dependence of thermodynamic and transport properties, particularly at low temperatures. Yet it is not yet known which of a number of likely possible candidates for superconducting pairing state is the appropriate model for Upt3. Separating intrinsic and extrinsic behavior is the key to solving this problem and is a challenge for experimental and theoretical condensed matter physics in concert with a materials program. Growing and characterizing the purest, most defect-free crystals possible is essential to the success of research in this field and we have developed facilities for this purpose. Interest has been expressed from an international group of scientists to collaborate with us, working with the materials produced in these facilities. The proposed work draws together four principal investigators, Professors Bedzyk, Halperin, Sauls and Seidman from two departments at Northwestern University: Materials Science and Engineering and Physics and Astronomy. These researchers have expertise in materials science, crystal growth and characterization, experimental low temperature physics, and theoretical physics of correlated electron systems and superconductivity. The expertise of the members of this group is at the forefront of their respective disciplines. ***

9705473 Halperin该计划的雄心勃勃的目标是了解重型费米亚化合物中超导性的机制。 第一步是确定顺序参数的对称性，我们首先将重点放在UPT3上，这可以说是原型非常规重费菲尔米式超导体。 为了确定UPT3中的配对状态，我们建议制作具有一系列杂质的单晶，并测量物理特性的杂质依赖性，包括导热率，比热和相图。 为了确定配对状态的自旋结构，我们将测量NMR骑士移位和上部临界场，并与对表面散射和强旋转轨道相互作用敏感的计算进行比较。 我们将进行磁化和磁化率的测量，并在其他机构的合作者使用中子和磁性X射线散射进一步研究磁相图。 我们将将这些结果与主要候选基态物理特性上的杂质和缺陷散射计算进行比较。 低温运输系数，例如 导热率很重要，因为它们反映了与间隙节点相关的低ENRGY激发。 我们认为，在高质量的单晶（例如我们能够生长）上进行的运输测量将在解决重型费米昂超导体中的配对状态的轨道对称性方面具有决定性作用，例如UPT3。 %%%提议解决重型费米昂超导性中的关键问题，最初关注重要的化合物UPT3。 这项研究的结果将影响对其他相关的费米亚超导体（尤其是高温超导体）中对超导性的理解。 UP T3中的超导性是非常规的，在其复杂的相图中很明显，并且在热力学和传输性能的温度依赖性中，尤其是在低温下的温度依赖性中所表现出的功率定律。 然而，尚不清楚多个可能的超导配对状态的可能候选者中的哪个是UPT3的适当模型。 分离内在和外在行为是解决此问题的关键，并且是与材料程序一致的实验和理论冷凝物理物理学的挑战。 生长和表征最纯净，最无缺陷的晶体可能对该领域的研究成功至关重要，我们为此开发了设施。 兴趣是由国际科学家组表达的，与我们合作，与这些设施中生产的材料合作。 拟议的工作吸引了四名主要研究人员Bedzyk教授，Halperin，Sauls和Seidman的西北大学两个系：材料科学与工程学以及物理和天文学。 这些研究人员在材料科学，晶体生长和表征，实验性低温物理学以及相关电子系统和超导性的理论物理学方面具有专业知识。 该小组成员的专业知识位于各自学科的最前沿。 ***