Materials Studies and Superconductivity of Uranium Platinum 3

[7054 . 73] Halperin这个项目雄心勃勃的目标是了解重费米子化合物的超导机制。第一步是确定序参数的对称性，我们首先关注Upt3，它可以说是非常规重费米子超导体的原型。为了确定Upt3中的配对状态，我们建议制作具有一定杂质范围的单晶，并测量物理性质的杂质依赖性，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NMR奈特位移和上临界场，并与表面散射和强自旋轨道相互作用敏感的计算结果进行比较。我们将进行磁化和磁电阻的测量，并与我们在其他机构的合作者一起，我们将利用中子和磁x射线散射进一步研究磁相图。我们将把这些结果与主要候选基态的杂质和缺陷散射计算结果进行比较。低温输运系数，如：热导率很重要，因为它们反映了与间隙节点相关的低能量激发。我们相信，在高质量单晶上的输运测量，如我们能够生长的，将对解决重费米子超导体（如Upt3）中配对态的轨道对称性起决定性作用。提出了解决重费米子超导的关键问题，首先关注重要的化合物Upt3。本研究结果将对其他相关费米子超导体，特别是高温超导体的超导性的认识产生影响。Up t3的超导性是非常规的，这在其复杂的相图和热力学和输运性质的温度依赖中表现出来的幂定律中是显而易见的，特别是在低温下。然而，目前还不知道在许多可能的超导配对状态候选者中，哪一个是适合Upt3的模型。分离内在和外在行为是解决这个问题的关键，也是实验和理论凝聚态物理与材料计划相结合的一个挑战。生长和表征最纯净、最无缺陷的晶体对该领域研究的成功至关重要，我们为此开发了设备。一个国际科学家小组表示有兴趣与我们合作，使用这些设施生产的材料。这项计划将四位主要研究人员聚集在一起，他们是西北大学材料科学与工程和物理与天文学两个系的Bedzyk、Halperin、Sauls和Seidman教授。这些研究人员在材料科学，晶体生长和表征，实验低温物理以及相关电子系统和超导的理论物理方面具有专业知识。该小组成员的专业知识处于各自学科的前沿。＊＊＊

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. ***