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

非技术摘要：本项目的目标是发展一个基本的理解的微观反应的强相关电子系统掺杂和压力。就其本质而言，这些材料对杂质高度敏感，掺杂剂经常用于调节其性能。 然而，很少有人知道掺杂剂原子附近的微观行为，以及杂质如何共同修改体特性。该研究项目采用核磁共振技术，使用最先进的金刚石砧压力单元探测高质量单晶。该项目的一个主要重点是研究生教育，它包括面向广大学生的教育推广活动。对当地一所小学开展的外联工作包括开展科学项目，积极让儿童参与科学方法，并通过大学推广办公室为成年和老年学生开设凝聚态科学课程。强关联电子材料为新技术提供了巨大的潜力，但对其相关多体物理学的基本理解仍然是凝聚态物理学中最大的挑战之一。化学掺杂被广泛用作调节这些材料基态的直接机制，经常揭示丰富的相图，包括非常规的超导性和非费米液体行为。 然而，在微观水平上，掺杂剂强烈地扰动电子自由度，在某些情况下引起非普遍的行为，如相分离和不均匀的玻璃态动力学。这些强烈不均匀的响应可以掩盖内在的现象，并使批量测量的解释复杂化。该项目通过对两个原型相关电子系统（铁磷属元素化物和重费米子超导体）的核磁共振研究，探讨掺杂和压力作为调谐参数之间的差异。该研究小组正在开发先进的新设备，以探索使用金刚石砧单元实现大的流体静力学压力的微观行为，并使用机械夹具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。这项研究的结果是一个更完整的理解如何在无序的存在下影响宏观性质的强相关性。

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.