Materials Studies and Superconductivity of Uranium Platinum 3

小行星9705473 该计划的雄心勃勃的目标是了解重费米子化合物的超导机制。 第一步是确定序参量的对称性，我们首先关注Upt3，它可以说是原型的非常规重费米子超导体。 为了确定Upt3中的配对状态，我们建议用一系列杂质制备单晶，并测量其相对密度。 杂质 物理依赖性 性能，包括导热系数，比热和相图。 为了确定配对态的自旋结构，我们将测量核磁共振骑士位移和上临界场，并与敏感的计算进行比较 表面散射和强自旋轨道相互作用。 我们将进行测量的磁化和磁阻，并与我们的合作者在其他机构，我们将进一步研究使用中子和磁X射线散射的磁相图。 我们将比较这些结果与杂质和缺陷散射的物理性质的计算， 主要候选人基态。 低温运输 系数，例如。 导热性， 是重要的，因为它们反映了与差距的节点相关联的低能激励。 我们相信，在我们能够生长的高质量单晶上的输运测量，将在解决重费米子超导体（例如Upt3）中配对态的轨道对称性方面起决定性作用。 提出了解决重费米子超导性中的关键问题，其初始焦点是重费米子超导性。 重要化合物Upt3。 这项研究的结果将对理解超导电性产生影响， 其他相关的费米子超导体，特别是高温超导体。 超导性 在 上t3 是非常规的，在其复杂的相图和温度依赖性中表现出的幂律中是显而易见的。 热力学和运输 性能，特别是在低温下。 然而，目前还不知道哪些可能的候选人， 对超导配对态的模型是Upt3的合适模型。 分离内在和外在行为是关键 这对实验和理论凝聚态物理学都是一个挑战 与 一 材料 程序. 增长 和表征 的 最纯净，最完美 晶体的可能性对于这一领域研究的成功至关重要，我们已经为此目的开发了设施。 一个国际科学家小组表示有兴趣与我们合作， 与 这些设施生产的材料。 这项工作吸引了四位主要研究人员，来自西北大学两个系的Bedzyk，Halperin，Sauls和Seidman教授：材料科学与工程和物理与天文学。 这些研究人员在材料科学，晶体生长和表征，实验， 低温物理学，以及 理论物理 的 相关 电子 系统 和超导性。 该小组成员的专业知识在各自学科中处于领先地位。 ***

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. ***