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: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=655516
• 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.

所有的电子、磁性和结构性质在两种材料（或表面）之间的界面附近改变，这是由于电子的平移对称性破缺和离域性质，其中电子波函数的特性作为离边界的距离的函数而变化。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，集体行为在许多纳米甚至微米范围内进行修改。磁性多层膜中的巨磁阻效应就是一个显著的例子，它对磁存储产生了巨大的影响。只有少数实验方法能够探测局部的磁性和电子性质的深度分辨的方式。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。另一个密切相关的方法是低能μ子自旋旋转/弛豫，它是由瑞士的保罗·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，以解决凝聚态物理学中的重要问题。这包括SrTiO 3/LaAlO 3界面的磁/电子性质，拓扑绝缘体的电磁响应以及高度关联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/磁性。研究结果将用于测试理论预测和寻找新现象。这反过来将有助于创造一个更统一的图像，即电子如何在低温下组织成物质的相干态，以及它们如何对界面附近和异质结构内的电场和磁场作出反应。潜在的影响来自于未来器件将越来越多地利用界面处和异质结构内的电子特性的预期。我们将使用新开发的低能量muSR和低能量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是在1957年沿着发现弱相互作用中的宇称破缺而发明的。然而，这里使用的特定变体相对较新，仍在发展中。关键点在于，与传统NMR不同，β-NMR和muSR中的信号与样品大小无关，并且可以作为nm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于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Korringa弛豫）更敏感，因为它的寿命更长（1.2s），而μ子的寿命为2.2微秒。