Novel Properties of Electrons Near Intefaces Studied with muSR and beta-NMR

使用 muSR 和 β-NMR 研究界面附近电子的新特性

• 批准号: RGPIN-2014-04428
• 负责人: Kiefl, Robert
• 金额: $ 3.06万
• 依托单位: University of British Columbia
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=566515
• 关键词: Novel; Properties; Electrons; Near; Intefaces

All electronic, magnetic and structural properties are altered near an interface between two materials (or a surface) due to the broken translational symmetry and delocalized nature of electrons in which the character of the electronic wavefunction varies as a function of distance from the boundary. In some cases these changes are small and confined to a few atomic layers while in other situations, the collective behaviour is modified over many nanometers or even microns. Giant magneto-resistance in magnetic multilayers is one notable example which had a dramatic impact on magnetic storage. Only a few experimental methods are capable of probing local magnetic and electronic properties in a depth resolved manner. We have developed one of them at TRIUMF called low energy beta-detected nuclear magnetic resonance (beta-NMR). Another closely related method is low energy muon spin rotation/relaxation, which has been developed at the Paul Scherrer Institute (PSI) in Switzerland. Both methods will be used to explore the coherent properties of electrons near interfaces and within heterostructures in order to address important problems in condensed matter physics. This includes the magnetic/electronic properties of the SrTiO3/LaAlO3 interface, the electromagnetic response of topological insulators and the depth dependence of the superconducting and magnetic order parameter in highly correlated systems. Our main objective is to explore/control the electronic/magnetic properties near the interfaces and surfaces of quantum materials. The results will be used to test theoretical predictions and search for new phenomena. This is turn will help create a more unified picture of how electrons organize themselves into coherent states of matter at low temperatures and how they respond to electric and magnetic fields near interfaces and within heterostructures. The potential impact comes from the expectation that future devices will increasingly utilize on the properties of electrons at interfaces and within heterostructures. We will use newly developed techniques of low energy muSR and low energy beta-NMR, which have similar principles but provide complementary information. The magnetic moment of the muon (or radioactive nucleus) acts as a probe of the local magnetic/electronic environment. Conventional muon spin rotation and beta-NMR were invented in 1957 along with the discovery of parity violation in weak interactions. However, the particular variants used here are relatively new and still developing. The key points are that unlike conventional NMR, the signals in beta-NMR and muSR are independent of sample size and can be monitored as a function depth on a nm length scale. Consequently both methods are ideally suited to studies of thin films and heterostructures. They are both forms of magnetic resonance but provide complementary information. The muon is a sensitive probe of static or quasi static magnetic fields whereas 8Li is much more sensitive to slow electronic relaxation processes (e.g.Korringa relaxation in a metal) due to the much longer lifetime (1.2s), compared to 2.2 microseconds for the muon.

由于电子的平移对称性破缺和离域性质，在两种材料（或表面）之间的界面附近，所有电子、磁性和结构特性都会发生改变，其中电子波函数的特性随着距边界的距离而变化。在某些情况下，这些变化很小，仅限于几个原子层，而在其他情况下，集体行为会在许多纳米甚至微米范围内发生变化。磁性多层中的巨磁阻是一个对磁存储产生巨大影响的著名例子。只有少数实验方法能够以深度解析的方式探测局部磁和电子特性。我们在 TRIUMF 开发了其中一种称为低能 β 检测核磁共振 (β-NMR) 的技术。另一种密切相关的方法是低能μ子自旋旋转/弛豫，它是由瑞士保罗谢勒研究所（PSI）开发的。这两种方法都将用于探索界面附近和异质结构内电子的相干特性，以解决凝聚态物理中的重要问题。这包括 SrTiO3/LaAlO3 界面的磁/电子特性、拓扑绝缘体的电磁响应以及高度相关系统中超导和磁序参数的深度依赖性。我们的主要目标是探索/控制量子材料界面和表面附近的电子/磁特性。结果将用于测试理论预测并寻找新现象。这反过来将有助于创建一个更统一的图景，了解电子如何在低温下将自己组织成相干物质态，以及它们如何响应界面附近和异质结构内的电场和磁场。潜在的影响来自于未来设备将越来越多地利用界面和异质结构内电子特性的预期。我们将使用新开发的低能 muSR 和低能 β-NMR 技术，它们具有相似的原理，但提供互补的信息。 μ子（或放射性核）的磁矩充当局部磁/电子环境的探针。传统的 μ 子自旋旋转和 β-NMR 于 1957 年发明，同时发现了弱相互作用中的宇称不守恒。然而，这里使用的特定变体相对较新并且仍在开发中。关键点是，与传统 NMR 不同，β-NMR 和 muSR 中的信号与样本大小无关，并且可以作为纳米长度尺度上的函数深度进行监测。因此，这两种方法都非常适合薄膜和异质结构的研究。它们都是磁共振的形式，但提供互补的信息。 μ 子是静态或准静态磁场的敏感探针，而 8Li 对缓慢的电子弛豫过程（例如金属中的科林加弛豫）更加敏感，因为它的寿命 (1.2 秒) 比 μ 子的 2.2 微秒长得多。