Pursuit of Quantum Spin Liquids in Exfoliated Anti-Ferromagnetic Insulators

在剥离反铁磁绝缘体中寻找量子自旋液体

• 批准号: 1810305
• 负责人: Erik Henriksen
• 金额: $ 40.64万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-01 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1810305&HistoricalAwards=false
• 关键词: Pursuit; Quantum; Spin; Liquids; Exfoliated

Nontechnical Abstract: Conducting materials display a host of fascinating properties, but remarkable behavior can persist even when conduction ceases. For example, electrons can behave roughly like small bar magnets, and one may roughly imagine the material as composed of arrays of magnets, fixed in place but each rotating in response to all the others. Usually this results in alignement of the magnets with their neighbors. In extremely rare cases, quantum mechanics inhibits the alignment of these electron magnets so their motion remains fluid; such a "quantum spin liquid" is one of the most highly sought after phenomena in modern condensed matter research and may hold the key to understanding potentially groundbreaking technologies like room temperature superconductivity. Recently, a quantum spin liquid has been proposed in a bulk material made of layered sheets of ruthenium chloride where the ruthenium atoms - each surrounded by many chlorines - support the magnetic behavior. Here, isolated individual flakes of this layered material (down to only one layer thick) are used to study the quantum spin liquid using techniques from the field of 2D physics. To build intuition for the physics of magnetism, a table-top system of freely rotating bar magnets is used as a demonstration in introductory physics courses. Finally, this work supports outreach programs to African-American middle and high school aged girls in the St. Louis area through a collaboration between the principal investigator and faculty in the Brown School of Social Work. Technical Abstract: Quantum spin liquids, as an ensemble of spins frustrated from achieving an ordered state, with dynamics dominated by quantum fluctuations, are an intriguing and highly sought after phase of magnetic quantum matter. The two-dimensional Kitaev quantum spin liquid (QSL) has recently been observed in the layered antiferromagnet RuCl3. This work focuses on exfoliation of RuCl3 flakes to few and single-layer systems seeking to stabilize the QSL by removing interlayer interactions. Several important milestones along the way will lead to new methods of investigating quantum magnetism, focusing in particular on antiferromagnetic proximity effects in layered devices. In particular the usual techniques to explore magnetism are extremely difficult to apply to microscopic samples, so a new set of probes is under development in which flakes of RuCl3, along with other antiferromagnetic materials of interest, are placed on graphene, with the goal of inducing a proximity effect in graphene. The electronic properties of graphene are impacted by the presence of antiferromagnetic exchange and readily explored via electronic transport (quantum Hall effects and non-local transport), optical (infrared magnetospectroscopy), and thermodynamic probes (electronic compressibility and magnetization). An electronic method of measuring magnetization in microscopic flakes is employed, opening a new window on thermodynamic physics of microscopic systems. The link between structure and magnetism is explored through studying a variety of heterostructure devices where the type, thickness, and stacking order of the layers is varied to control interlayer magnetic couplings.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术摘要：导电材料显示出许多迷人的特性，但即使在导电停止时，显着的行为也会持续下去。例如，电子的行为可以大致类似于小条形磁铁，人们可以大致想象材料由磁铁阵列组成，固定在原地，但每个磁铁都响应所有其他磁铁而旋转。通常这会导致磁体与其相邻磁体的相互作用。在极少数情况下，量子力学会抑制这些电子磁体的排列，使它们的运动保持流动;这种“量子自旋液体”是现代凝聚态研究中最受追捧的现象之一，可能是理解室温超导等潜在突破性技术的关键。最近，量子自旋液体已经被提出在由氯化钌的层状薄片制成的块状材料中，其中钌原子-每个被许多氯包围-支持磁性行为。在这里，这种分层材料的孤立的单个薄片（只有一层厚）被用于使用2D物理学领域的技术研究量子自旋液体。为了建立对磁性物理的直觉，一个自由旋转的条形磁铁的桌面系统被用作入门物理课程的演示。最后，这项工作支持外展计划，以非洲裔美国初中和高中年龄的女孩在圣路易斯地区通过首席研究员和教师之间的合作，在布朗社会工作学院。技术摘要：量子自旋液体，作为一种自旋的集合，从实现一个有序的状态，与量子涨落占主导地位的动力学，是一个有趣的和备受追捧的磁量子物质相。二维Kitaev量子自旋液体（QSL）最近在层状反铁磁体RuCl 3中被观察到。这项工作的重点是剥离的RuCl 3薄片，以少数和单层系统，寻求稳定的QSL通过消除层间相互作用。沿着这条道路的几个重要里程碑沿着将导致研究量子磁性的新方法，特别是在分层设备中的反铁磁邻近效应。特别是通常的磁性探测技术很难应用于微观样品，因此一组新的探针正在开发中，其中RuCl 3的薄片，沿着其他感兴趣的反铁磁材料，被放置在石墨烯上，目的是在石墨烯中诱导邻近效应。石墨烯的电子性质受到反铁磁交换的影响，并且容易通过电子输运（量子霍尔效应和非局域输运），光学（红外磁谱）和热力学探针（电子压缩性和磁化）进行探索。采用电子方法测量微观薄片的磁化强度，为微观系统的热力学物理研究打开了一扇新的窗口。结构和磁性之间的联系是通过研究各种异质结构器件来探索的，这些异质结构器件的类型、厚度和堆叠顺序是不同的，以控制层间磁耦合。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Extraordinary magnetoresistance in encapsulated monolayer graphene devices

封装单层石墨烯器件中的非凡磁阻

• DOI: 10.1063/1.5142021
• 发表时间: 2020
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Zhou, Bowen;Watanabe, K.;Taniguchi, T.;Henriksen, E. A.
• 通讯作者: Henriksen, E. A.

Modulation Doping via a Two-Dimensional Atomic Crystalline Acceptor

• DOI: 10.1021/acs.nanolett.0c03493
• 发表时间: 2020-12-09
• 期刊: NANO LETTERS
• 影响因子: 10.8
• 作者: Wang, Yiping;Balgley, Jesse;Burch, Kenneth S.
• 通讯作者: Burch, Kenneth S.