Collaborative Research: Coherent Transport in the One-Dimensional limit

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。*非技术摘要*这个合作项目将研究电子介观结构的物理。这些结构由大量原子组成，但足够小，足以显示宏观物体中没有的量子现象。从基础物理学的角度来看，了解较小的尺寸如何影响电子性质是一个有趣的问题，也是朝着更快、更小的电子学的进步迈出的重要一步，甚至可能利用这种量子现象。正在研究的特定结构是用碳纳米管制成的，它由一层包裹在圆柱体形状的碳原子层组成，直径大约是人类头发直径的10万倍。由于量子力学，沿着纳米管传播的电荷表现为波，而连接到纳米管的多个电极表现为浅而窄的池塘中的岩石，阻碍波传播并引起反射和涟漪。这个项目将研究这些现象如何影响电学特性。它还将研究当样本大小减少到如此小的维度时，是否会出现新的物质状态。更具体地说，它将调查碳纳米管是否以及在什么条件下可能成为新型超导材料。如果成功，这项研究将为超导的新机制以及如何控制超导性质提供亟需的见解，可能为发现在接近室温的温度下工作的超导体铺平道路。这一计划的教育影响远远超出了博士后研究员和从事该项目的研究生的直接支持。在非科学专业和物理专业的课程中，通过介绍纳米技术和高分辨率显微镜的讲座，与这项研究的联系不断发展。*技术摘要*碳纳米管是研究低维、相位相干输运性质的理想介观对象，因为很容易实现小于相位相干长度(约1微米)的结构。本项目将集中对相干输运的三种表现形式进行实验和理论研究：1)纳米管已被证明是相干电子波导。这个项目将探索单个纳米管上的多个电极如何在纳米管中产生多个驻波并影响传输特性，包括非局域效应，其中一个纳米管部分的传输受到相邻部分的影响；2)通过正常的金属层连接到超导电极的纳米管是最小的点接触，它们可以检测到纳米尺度上由于超导邻近效应而产生的相干传输。这一效应将被用来研究碳纳米管/正常金属界面的性质如何取决于电极材料和接触化学物质；以及3)该项目将研究当施加栅极电压时，单个单壁碳纳米管中可能发生的超导现象。这种效应将在单纳米管和多纳米管薄膜中进行研究。这个项目的教育影响远远超出了博士后研究员和参与该项目的研究生的直接支持，因为与这项研究的联系在非理科专业和物理专业的课程中不断发展。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).****NON-TECHNICAL ABSTRACT****This collaborative project will investigate the physics of electronic mesoscopic structures. These structures are made of a large number of atoms, but are sufficiently small to exhibit quantum phenomena that are not found in macroscopic objects. Understanding how the smaller size affects electronic properties is an intriguing problem from the standpoint of basic physics, as well as an essential step towards progress for faster and smaller electronics, that can even possibly exploit such quantum phenomena. The specific structures being investigated are made with carbon nanotubes, consisting of a layer of carbon atoms wrapped in the shape of a cylinder, with a diameter approximately 100,000 times smaller than the diameter of a human hair. Due to quantum mechanics, charges propagating along the nanotube behave like waves, whereas multiple electrodes connected to the tube behave like rocks in a shallow and narrow pond, obstructing wave propagation and causing reflections and ripples. This project will study how these phenomena affect electrical properties. It will also study whether novel states of matter could arise when the sample size is reduced to such small dimensions. More specifically, it will investigate whether and under which conditions carbon nanotubes may be novel superconducting materials. If successful, this study will provide much needed insight on new mechanisms for superconductivity and how to control superconducting properties, possibly paving the way towards the discovery of superconductors that work at temperatures close to room temperatures. The educational impact of this program goes well beyond the direct support of the postdoctoral fellow and the graduate student working on the project. Connections with this research are continuously developed in courses for non-science majors and physics majors, by introducing lectures on nanotechnology and high-resolution microscopy.**** TECHNICAL ABSTRACT****Carbon nanotubes are ideal mesoscopic objects to study properties of low-dimensional, phase coherent transport, because structures smaller than the phase coherence length (on the order of 1 micrometer) can be easily realized. This project will focus on a combined experimental and theoretical investigation of three manifestations of coherent transport:1) Nanotubes have been shown to act as coherent electron waveguides. This project will probe how multiple electrodes on a single nanotube create multiple standing waves in the nanotube and affect transport properties, including non-local effects, where transport in one nanotube section is affected by the adjacent sections; 2) Nanotubes connected to superconducting electrodes through a normal metal layer are the smallest point contacts and they can detect coherent transport due to the superconducting proximity effect at the nanometer scale. This effect will be used to study how the properties of the carbon-nanotube/normal-metal interface depend on the electrode material and on exposure to chemicals; and 3) The project will investigate the possible occurrence of superconductivity in individual single-walled carbon nanotubes when the gate voltage is applied. This effect will be studied in single nanotubes as well as in films of multiple nanotubes. The educational impact of this program goes well beyond the direct support of the postdoctoral fellow and the graduate student working on the project, as connections with this research are continuously developed in courses for non-science majors and physics majors.