Topics in Quantum Magnetism, Nanoelectronics and Superconductivity

量子磁学、纳米电子学和超导主题

• 批准号: 0203159
• 负责人: Antonio Castro-Neto
• 金额: --
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2004-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0203159&HistoricalAwards=false
• 关键词: Topics; Quantum; Magnetism; Nanoelectronics; Superconductivity

This award supports theoretical research and education in condensed matter physics centered on three related areas: quantum magnetism, nanoelectronics and superconductivity.Although a classical view of magnetism is often successful, it fails badly in certain cases, in particular for quasi-one-dimensional (1D) systems where the atomic spins interact much more strongly along chains in a crystal than between chains. From a classical viewpoint, at zero temperature the atomic spins would align in fixed directions ("up "and "down "). This often doesn't occur in low dimensional systems. Instead, strongly quantum mechanical groundstates occur, in which the spins are in collective linear superpositions of up and down. In recent years this has become a very active experimental field, with numerous examples of quasi-one-dimensional antiferromagnets being synthesized and studied by increasingly refined techniques. This is motivated in part by the connection of these materials, and some of the phenomena that occur in them, with high-temperature superconductivity and spintronics. The PI will continue developing fundamental theory and useful phenomenology for understanding current experiments on various quasi-one-dimensional and quasi-two-dimensional magnetic insulators.As electronic components continue to miniaturize, a limit approaches where the largely classical views of memory elements, transistors, etc. break down and quantum mechanics plays a crucial role. In particular, remarkable quantum phenomena have been recently observed in "single electron transistors "or quantum dots, where the number of electrons on the dot can be varied in single steps. Such nano-engineered devices can exhibit behavior previously studied in atomic impurities doped into metals, with the quantum dot playing the role of a single atomic spin. Such a spin gets "screened " by an electron from the metal (or the leads connected to the quantum dot). It has been claimed that this screening electron is spread out over a very large distance, of order .1-1 microns. This large length scale has never been verified experimentally and has been a source of theoretical confusion. Quantum dots provide unique opportunities to finally observe this Kondo screening cloud. The PI will develop a theoretical understanding of this screening cloud and aims to propose realistic devices and experiments whereby it could be measured.The high-temperature superconductors hold out the promise of important technological applications and, at the same time, raise very difficult fundamental science issues. The will address several theoretical issues in this field. In particular, by collaborating with experts on large scale numerical simulations, he intends to study the possibility of holes arranging themselves into narrow "stripes "separated y insulating antiferromagnetic regions in some of these materials (and in some models used to study them). How generally this occurs, for what reasons and whether it hinders or helps superconductivity are important open questions in the field.%%%This award supports theoretical research and education in condensed matter physics centered on three related areas: quantum magnetism, nanoelectronics and superconductivity.Although a classical view of magnetism is often successful, it fails badly in certain cases, in particular for quasi-one-dimensional (1D) systems where the atomic spins interact much more strongly along chains in a crystal than between chains. From a classical viewpoint, at zero temperature the atomic spins would align in fixed directions (say, "up "and "down "). This often doesn't occur in low dimensional systems. Instead, strongly quantum mechanical groundstates occur, in which the spins are in collective linear superpositions of up and down. In recent years this has become a very active experimental field, with numerous examples of quasi-one-dimensional antiferromagnets being synthesized and studied by increasingly refined techniques. This is motivated in part by the connection of these materials, and some of the phenomena that occur in them, with high-temperature superconductivity and spintronics. The PI will continue developing fundamental theory and useful phenomenology for understanding current experiments on various quasi-one-dimensional and quasi-two-dimensional magnetic insulators.As electronic components continue to miniaturize, a limit approaches where the largely classical views of memory elements, transistors, etc. break down and quantum mechanics plays a crucial role. In particular, remarkable quantum phenomena have been recently observed in "single electron transistors "or quantum dots, where the number of electrons on the dot can be varied in single steps. Such nano-engineered devices can exhibit behavior previously studied in atomic impurities doped into metals, with the quantum dot playing the role of a single atomic spin. Such a spin gets "screened " by an electron from the metal (or the leads connected to the quantum dot). It has been claimed that this screening electron is spread out over a very large distance, of order .1-1 microns. This large length scale has never been verified experimentally and has been a source of theoretical confusion. Quantum dots provide unique opportunities to finally observe this Kondo screening cloud. The PI will develop a theoretical understanding of this screening cloud and aims to propose realistic devices and experiments whereby it could be measured.The high-temperature superconductors hold out the promise of important technological applications and, at the same time, raise very difficult fundamental science issues. The will address several theoretical issues in this field. In particular, by collaborating with experts on large scale numerical simulations, he intends to study the possibility of holes arranging themselves into narrow "stripes "separated by insulating antiferromagnetic regions in some of these materials (and in some models used to study them). How generally this occurs, for what reasons and whether it hinders or helps superconductivity are important open questions in the field.***

该奖项支持凝聚态物理的理论研究和教育，集中在三个相关领域：量子磁性、纳米电子学和超导性。尽管磁性的经典观点通常是成功的，但在某些情况下会严重失败，特别是对于准一维（1D）系统，其中原子自旋沿晶体链的相互作用比链之间的相互作用更强。从经典的角度来看，在零温度下，原子自旋将沿固定方向（“向上”和“向下”）排列。这通常不会发生在低维系统中。相反，会出现强量子力学基态，其中自旋呈上下集体线性叠加。近年来，这已成为一个非常活跃的实验领域，通过日益完善的技术合成和研究了许多准一维反铁磁体的例子。这在一定程度上是由于这些材料以及其中发生的一些现象与高温超导性和自旋电子学的联系所推动的。 PI 将继续发展基础理论和有用的现象学，以理解当前各种准一维和准二维磁绝缘体的实验。随着电子元件不断小型化，存储元件、晶体管等的大部分经典观点将被打破，量子力学将发挥至关重要的作用。特别是，最近在“单电子晶体管”或量子点中观察到了显着的量子现象，其中点上的电子数量可以一步改变。这种纳米工程器件可以表现出先前在金属中掺杂的原子杂质中研究的行为，其中量子点扮演单个原子自旋的角色。这种自旋被来自金属（或连接到量子点的引线）的电子“屏蔽”。据称，这种屏蔽电子分布在非常大的距离上，数量级为 0.1-1 微米。这种大长度尺度从未经过实验验证，并且一直是理论混乱的根源。量子点提供了最终观察近藤屏蔽云的独特机会。 PI 将发展对这种屏蔽云的理论理解，并旨在提出可对其进行测量的现实设备和实验。高温超导体有望实现重要的技术应用，同时提出非常困难的基础科学问题。它将解决该领域的几个理论问题。特别是，通过与大规模数值模拟专家合作，他打算研究其中一些材料（以及用于研究它们的一些模型）中孔排列成狭窄“条纹”分隔绝缘反铁磁区域的可能性。这种现象通常是如何发生的、出于什么原因以及它是否阻碍或帮助超导性是该领域中重要的开放性问题。%%%该奖项支持以三个相关领域为中心的凝聚态物理理论研究和教育：量子磁性、纳米电子学和超导性。尽管磁性的经典观点通常是成功的，但在某些情况下会严重失败，特别是对于准一维（1D）系统，其中 晶体中原子自旋沿着链的相互作用比链之间的相互作用更强烈。从经典的角度来看，在零温度下，原子自旋将沿固定方向排列（例如“向上”和“向下”）。这通常不会发生在低维系统中。相反，会出现强量子力学基态，其中自旋呈上下集体线性叠加。近年来，这已成为一个非常活跃的实验领域，通过日益完善的技术合成和研究了许多准一维反铁磁体的例子。这在一定程度上是由于这些材料以及其中发生的一些现象与高温超导性和自旋电子学的联系所推动的。 PI 将继续发展基础理论和有用的现象学，以理解当前各种准一维和准二维磁绝缘体的实验。随着电子元件不断小型化，存储元件、晶体管等的大部分经典观点将被打破，量子力学将发挥至关重要的作用。特别是，最近在“单电子晶体管”或量子点中观察到了显着的量子现象，其中点上的电子数量可以一步改变。这种纳米工程器件可以表现出先前在金属中掺杂的原子杂质中研究的行为，其中量子点扮演单个原子自旋的角色。这种自旋被来自金属（或连接到量子点的引线）的电子“屏蔽”。据称，这种屏蔽电子分布在非常大的距离上，数量级为 0.1-1 微米。这种大长度尺度从未经过实验验证，并且一直是理论混乱的根源。量子点提供了最终观察近藤屏蔽云的独特机会。 PI 将发展对这种屏蔽云的理论理解，并旨在提出可对其进行测量的现实设备和实验。高温超导体有望实现重要的技术应用，同时提出非常困难的基础科学问题。它将解决该领域的几个理论问题。特别是，通过与大规模数值模拟专家合作，他打算研究孔排列成狭窄“条纹”的可能性，这些“条纹”由其中一些材料中的绝缘反铁磁区域分隔开（以及在用于研究它们的一些模型中）。这种现象通常如何发生、原因是什么以及它是否阻碍或有助于超导性是该领域重要的悬而未决的问题。***