High Pressure NMR Studies of Doping and Inhomogeneity in Strongly Correlated Electron Systems

非技术摘要：本项目的目标是对强关联电子系统对掺杂和压力的微观响应有一个基本的了解。就其性质而言，这些材料对杂质高度敏感，掺杂剂经常被用来调整它们的性能。然而，关于掺杂原子附近的微观行为，以及杂质如何集体改变整体性质，人们知之甚少。该研究项目采用核磁共振技术，使用最先进的金刚石顶锤压力室探测高质量的单晶。该项目的一个主要重点是研究生教育，它纳入了面向广泛学生的教育推广活动。对当地一所小学的外联努力包括积极让儿童参与科学方法的科学项目，以及通过大学推广办公室为成人和老年人学生开设的凝聚态科学课程。技术摘要：强关联电子材料具有巨大的新技术潜力，但对其相关多体物理的基本理解仍然是凝聚态物理中最大的挑战之一。化学掺杂被广泛用于调节这些材料的基态，通常揭示了丰富的相图，包括非传统的超导和非费米液体行为。然而，在微观层面上，掺杂强烈地扰动了电子的自由度，在某些情况下导致了非普遍的行为，如相分离和不均匀的玻璃动力学。这些强烈的不均匀反应可能会掩盖内在现象，并使整体测量的解释复杂化。这个项目通过对两个典型的相关电子系统：铁离子超导体和重费米子超导体的核磁共振研究，解决了掺杂和压强之间的差异作为调整参数。该研究小组正在开发先进的新设备，以探索微观行为，使用钻石砧座单元来实现大的流体静压，并使用机械夹具来实现单晶的单轴应变。这两种技术都可以在以前从未用磁共振研究过的条件下研究材料的微观响应。这项研究的结果是更完整地理解了无序存在时的强关联如何影响宏观性质。

Nontechnical abstract:The objective of this project is to develop a fundamental understanding of the microscopic response of strongly correlated electron systems to doping and pressure. By their very nature, these materials are highly sensitive to impurities, and dopants are frequently used to tune their properties. However, little is known about the microscopic behavior in the vicinity of dopant atoms, and how the impurities collectively modify bulk properties. This research project employs Nuclear Magnetic Resonance to probe high quality single crystals using a state-of-the-art diamond anvil pressure cell. A key focus of this project is graduate education, and it incorporates educational outreach activities to a broad range of students. Outreach efforts to a local elementary school include science projects that actively engage children in the scientific method and a course on condensed matter science for adult and senior citizen students through the university extension office. Technical abstract:Strongly correlated electron materials hold tremendous potential for new technologies, but a fundamental understanding of their relevant many-body physics remains one of the greatest challenges in condensed matter physics. Chemical doping is widely used as a straightforward mechanism to tune the ground state of these materials, often revealing rich phase diagrams including unconventional superconductivity and non-Fermi liquid behavior. At the microscopic level, however, dopants strongly perturb the electronic degrees of freedom, in some cases giving rise to non-universal behaviors such as phase segregation and inhomogeneous glassy dynamics. These strongly inhomogeneous responses can mask intrinsic phenomena, and complicate the interpretation of bulk measurements. This project addresses the differences between doping and pressure as tuning parameters through Nuclear Magnetic Resonance studies of two prototypical correlated electron systems: the iron pnictide and heavy fermion superconductors. The research team is developing advanced new equipment to explore the microscopic behavior using diamond anvil cells to achieve large hydrostastic pressures, and mechanical clamps to achieve uniaxial strain in single crystals. Both techniques enable the study of the microscopic response of materials under conditions that have never been investigated with magnetic resonance previously. The outcome of this research is a more complete understanding how strong correlations in the presence of disorder influence macroscopic properties.