CMP: Charge Fractionalization and Spin Charge Separation in One Dimensional Conductors

****非技术摘要****物质是由基本构件构成的。这些可能是基本粒子，比如构成中子和质子的夸克。它们可能不那么基本，就像描述晶体结构时的原子一样。此外，根据描述的水平，它们甚至可以是简单的基本激励模式，如描述吉他弦的振动。确定相关的构建模块并揭示其属性是形成我们对物质的描述和理解的必要步骤。在电子系统中，例如传统金属，电子本身构成了描述其许多特性（如导电性和热容量）的基本构件。尽管它们的数量庞大，并且它们之间存在电相互作用（称为库仑相互作用），但电子继续表现为独立的粒子，具有一个单位的电荷和一种称为自旋的磁性。令人惊讶的是，这种被称为费米液体理论的电子系统的简单描述，只在二维和三维空间中有效。在一维金属中，电子被迫沿着直线运动，库仑相互作用的包含完全打破了单粒子描述。一维系统的基本组成部分可以独立携带自旋和电荷，而载流子被分割成比一个电子电荷的单位还要小的数量。该项目旨在通过使用最先进的实验技术来研究新的一维系统，了解这些基本构建块在一维世界中的本质。这个项目教育学生在基本凝聚态物理和纳米科学的更多应用方面之间的接口。该研究的跨学科特性将培养出习惯于跨学科交流的学生。随着基础科学和应用科学相互接近，这些技能变得越来越重要。****技术摘要****量子一维（1D）系统可以携带比单个电子电荷更小的单位电荷。这种独特的效应是电子-电子相互作用的排斥性库仑的结果。根据描述这种系统的低能激发的Luttinger液体理论，在费米点附近添加的电子预计会分解成两个反向传播的电荷激发，携带电荷Q(+)=(1+g)/2和Q(-)=(1-g)/2，其中g1表示排斥相互作用。在实验中观察分馏物理是一个相当大的挑战。一个众所周知的例子是分数量子霍尔（FQH）态的基本激发。这些进位分数的形式是1/m， m是一个奇数。然而，量子线中所预测的电荷分馏尚未在实验中观察到。本计画利用一种新技术直接测量量子线中的电荷分馏。将使用双线几何。通过在两根导线之间的隧穿过程中的动量守恒，单向电子将被注入到导线的主体中，分块化导致在注入区域的两侧都检测到电流。这些电流的比率加上2端参考测量将能够确定电荷分馏的程度及其对各种系统参数（如载流子密度和无序度）的依赖。这个具有挑战性的项目教育学生在基本凝聚态物理和纳米科学的更多应用方面之间的接口。该研究的跨学科特性将培养出习惯于跨学科交流的学生。随着基础科学和应用科学相互接近，这些技能变得越来越重要。

****NON-TECHNICAL ABSTRACT****Matter is constructed from fundamental building blocks. These may be the elementary particles like quarks that construct neutrons and protons. They may be less fundamental, like the atoms when describing the structure of crystals. Moreover, depending on the level of description, they may even be simply fundamental excitation modes such as those describing the vibration of a guitar string. Identifying the relevant building blocks and unraveling their properties is an essential step in formulating our description and understanding of matter. In electronic systems, such as conventional metals, the electrons themselves constitute the elementary building block for the description of many of its properties such as the electrical conductivity and heat capacity. Despite their vast number and the electrical interaction (known as the Coulomb interaction) amongst them, the electrons continue to behave as independent particles with one unit of charge and a magnetic property called spin. Surprisingly, such a simple description of electronic systems, known as Fermi liquid theory, is valid only in two and three spatial dimensions. In one-dimensional metals, where electrons are forced to move along a straight line, the inclusion of Coulomb interactions completely breaks the single particle description. The elementary building blocks of a one-dimensional system can carry independently spin and charge and the charge carriers are fractionalized into quantities that are smaller than the unit of an electron charge. This project seeks to understand the nature of these elementary building blocks present in the one-dimensional world, by using state of the art experimental techniques to investigate novel one-dimensional systems. This project educates students at the interface between fundamental condensed matter physics and the more applied aspects of Nano-Science. The interdisciplinary character of the research will produce students who are used to communicating across disciplines. Such skills are of ever greater importance as fundamental and applied sciences approach one another.**** TECHNICAL ABSTRACT****Quantum one-dimensional (1D) systems can carry charge in units smaller than a single electron charge. This unique effect is a result of the repulsive Coulomb electron-electron interactions. According to Luttinger Liquid theory, which describes the low-energy excitations of such systems, an electron added near either Fermi point is expected to decompose into two counter propagating charge-excitations carrying charges Q(+)=(1+g)/2 and Q(-)=(1-g)/2 where g1 for repulsive interactions. Observing fractionalization physics in an experiment is a considerable challenge. A well-known example is the elementary excitations of the Fractional Quantum Hall (FQH) state. These carry charge fractions of the form 1/m, m being an odd integer. However, the predicted charge fractionalization in quantum wires has not been observed experimentally. This project utilizes a novel technique for direct measurement of charge fractionalization in quantum wires. A double-wire geometry will be used. Through momentum conservation in the tunneling process between the two wires, unidirectional electrons will be injected into the bulk of a wire, with fractionalization resulting in currents detected on both sides of the injection region. The ratio of these currents together with a 2-terminal reference measurement would enable the determination of the extent of charge fractionalization and its dependence on various system parameters such as the carrier density and disorder. This challenging project educates students at the interface between fundamental condensed matter physics and the more applied aspects of Nano-Science. The interdisciplinary character of the research will produce students who are used to communicating across disciplines. Such skills are of ever greater importance as fundamental and applied sciences approach one another.