Spatiotemporal Measurements of the Kondo Cloud

近藤云的时空测量

• 批准号: 1608962
• 负责人: David Goldhaber-Gordon
• 金额: $ 33.9万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1608962&HistoricalAwards=false
• 关键词: Spatiotemporal; Measurements; Kondo; Cloud

Non-Technical AbstractMaterials at the focus of modern physics research often feature competition among several ways electrons can organize. This is both a blessing and a curse, opening rich possibilities but also hindering basic understanding of these materials. What if one could build an experimental system which displays the key features believed to drive behavior of a material of interest, while discarding other effects which might obscure the fundamental mechanism?Modern technology such as transistors and lasers depends on the fact that adding even a small amount of impurities to a material can drastically alter its properties. Another example of such sensitivity is the Kondo effect: a few parts per million of magnetic impurities added to a metal drastically change its low-temperature electrical behavior. Such an impurity creates a "cloud" of electrons around it, which shields the magnetic moment of the impurity. This project aims to nanofabricate a device to measure the spatial extent of this cloud, and to study the competition between impurity-cloud and impurity-impurity interactions when two such impurities are brought together. This will shed light on a class of materials known as heavy fermion metals, in which exactly this competition is suspected to be key, by realizing the competition in a simplified and highly-controllable system.In addition to the research component, both the principal investigator and the students have a track record and plans for active involvement in outreach regarding nanoscience, including short programs for middle school teachers, and involving high school and college students in research.Technical AbstractThis project aims to determine the spatial extent of the Kondo screening cloud and study the Kondo-RKKY competition using a carefully-engineered model system based on gate-defined quantum dots in a GaAs/AlGaAs heterostructure. While the Kondo effect has been seen and studied in many different systems, a clear measurement of its spatial extent is still lacking. In the proposed device, the competition between the inter-impurity interaction and the impurity-bath interaction, suspected to be key to the behavior of several heavy-fermion compounds, is gate-tunable. Realizing the effect in a much more controllable nanostructure may elucidate the rich behavior occurring in those materials, including a quantum phase transition which could play a key role.As a complement to precision transport studies, a scanning gate experiment, where a metallic tip is scanned over the surface of a nanopatterned bilayer heterostructure, can perturb the Kondo cloud at a controlled location, providing a direct mapping of the spatial extent of a quantum many-body state.

摘要现代物理研究的焦点材料往往以电子组织方式的竞争为特征。这既是一种祝福也是一种诅咒，开启了丰富的可能性，但也阻碍了对这些材料的基本理解。如果一个人能建立一个实验系统，显示出被认为是驱动一种感兴趣的材料行为的关键特征，同时抛弃其他可能模糊基本机制的影响，会怎么样？晶体管和激光等现代技术依赖于这样一个事实：即使在材料中加入少量杂质，也能极大地改变其特性。这种敏感性的另一个例子是近藤效应：将百万分之几的磁性杂质添加到金属中，会极大地改变金属的低温电学行为。这样的杂质会在其周围形成一个电子“云”，从而屏蔽杂质的磁矩。本项目旨在纳米制造一种设备来测量该云的空间范围，并研究当两种杂质聚集在一起时，杂质-云和杂质-杂质相互作用之间的竞争。这将揭示一类被称为重费米子金属的材料，通过在一个简化和高度可控的系统中实现竞争，这种竞争被怀疑是关键。除了研究部分，首席研究员和学生都有积极参与纳米科学外展的记录和计划，包括为中学教师提供的短期课程，以及让高中生和大学生参与研究。本项目旨在确定Kondo筛选云的空间范围，并使用基于GaAs/AlGaAs异质结构中门定义量子点的精心设计的模型系统研究Kondo- rkky竞争。虽然在许多不同的系统中已经看到和研究了近藤效应，但仍然缺乏对其空间范围的明确测量。在所提出的装置中，杂质间相互作用和杂质-槽相互作用之间的竞争是门可调谐的，被怀疑是几种重费米子化合物行为的关键。在更可控的纳米结构中实现这种效应，可能会解释这些材料中发生的丰富行为，包括可能起关键作用的量子相变。作为精确输运研究的补充，扫描门实验，在纳米图案双层异质结构的表面扫描金属尖端，可以在受控位置扰动近藤云，提供量子多体态的空间范围的直接映射。