Spin Coherence and Magnetism in Graphene

石墨烯中的自旋相干性和磁性

• 批准号: 1007057
• 负责人: Roland Kawakami
• 金额: $ 36万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1007057&HistoricalAwards=false
• 关键词: Spin; Coherence; Magnetism; Graphene

****NON-TECHNICAL ABSTRACT****Electrons possess a fundamental property known as spin, which makes the electron equivalent to a small magnet. The long term goal of this project is to develop a powerful new type of computer known as a "spin computer" that uses the electron spin to store and process data. The design of this type of computer has been developed for electron spins in semiconductors, but such efforts have been hampered by small signals and the need for cryogenic (very low) operating temperatures. The advent of a new electronic material known as graphene, a single atomic sheet of carbon, is making the prospects of a spin computer more realistic because large spin signals have been demonstrated at room temperature. This project will advance the fundamental knowledge of electron spin in graphene by performing experiments that investigate the role of imperfections such as impurities, vacancies, and ripples in the graphene sheet. These studies are crucial because imperfections are believed to be responsible for the loss of information held by the electron spin ("decoherence"), although it is currently unclear which type of imperfection is the main source of the problem. The experiments will systematically address this critical issue and also explore new methods of using the imperfections to control the alignment of the spins ("magnetism"). This project will support the training of a PhD student, an undergraduate student, and a high school student in condensed matter physics using state-of-the-art instrumentation. The knowledge gained in these studies will greatly broaden the scientific and technological impact of spintronics.****TECHNICAL ABSTRACT****The origin of spin scattering in graphene is a central issue of graphene spintronics, while tunable magnetism is a fascinating collective phenomena predicted for doped and/or defective graphene. This project investigates spin scattering and tunable magnetism by systematically introducing impurities, vacancies, and ripples into graphene spin valves and Hall bar devices. The experimental approach combines the techniques of molecular beam epitaxy (MBE) and magnetotransport measurements in a unique manner. Impurities will be systematically introduced atom-by-atom through MBE deposition while vacancies will be generated by Ar-ion sputtering in an ultrahigh vacuum chamber. Their effect on charge and spin transport will be measured in the same chamber via in situ magnetotransport measurements. Ripples will be controlled through the use of atomically flat substrates produced by MBE. The effects of these types of disorder on spin lifetimes will be measured by spin precession (Hanle) measurements on spin valves and will elucidate the mechanism of spin scattering in graphene. The Kondo effect and gate tunable magnetic ordering in doped and/or defective graphene will be investigated through a combination of magnetotransport measurements and magnetization measurements. These experiments will greatly expand the knowledge of spin-dependent interactions in solid-state systems and provide excellent training for a PhD student, an undergraduate student, and a high school student in condensed matter physics.

* 非技术性摘要 * 电子具有一种称为自旋的基本性质，这使得电子相当于一个小磁铁。该项目的长期目标是开发一种功能强大的新型计算机，称为“自旋计算机”，它使用电子自旋来存储和处理数据。这种类型的计算机的设计是为半导体中的电子自旋而开发的，但这种努力受到小信号和对低温（非常低）工作温度的需求的阻碍。一种被称为石墨烯的新电子材料的出现，使自旋计算机的前景更加现实，因为在室温下已经证明了大的自旋信号。该项目将通过进行实验来研究石墨烯片中杂质，空位和波纹等缺陷的作用，从而推进石墨烯中电子自旋的基础知识。这些研究是至关重要的，因为不完美被认为是电子自旋（“退相干”）信息丢失的原因，尽管目前还不清楚哪种类型的不完美是问题的主要来源。这些实验将系统地解决这个关键问题，并探索使用不完美来控制自旋（“磁性”）对齐的新方法。该项目将支持使用最先进的仪器对一名博士生、一名本科生和一名高中生进行凝聚态物理学方面的培训。在这些研究中获得的知识将大大拓宽自旋电子学的科学和技术影响。石墨烯中自旋散射的起源是石墨烯自旋电子学的中心问题，而可调磁性是针对掺杂和/或缺陷石墨烯预测的迷人的集体现象。本项目通过在石墨烯自旋阀和霍尔棒器件中系统地引入杂质、空位和波纹来研究自旋散射和可调磁性。实验方法结合了分子束外延（MBE）和磁输运测量技术在一个独特的方式。杂质将通过MBE沉积系统地一个原子接一个原子地引入，而空位将通过Ar离子溅射在一个真空室中产生。它们对电荷和自旋输运的影响将在同一个腔室中通过原位磁输运测量来测量。波纹将通过使用分子束外延生产的原子级平面衬底来控制。这些类型的无序对自旋寿命的影响将通过自旋阀上的自旋进动（Hanle）测量来测量，并将阐明石墨烯中自旋散射的机制。近藤效应和门可调磁有序掺杂和/或有缺陷的石墨烯将通过磁输运测量和磁化测量的组合进行研究。这些实验将极大地扩展固态系统中自旋相关相互作用的知识，并为博士生，本科生和高中生提供凝聚态物理学的优秀培训。