Nonequilibrium Phenomena in Mesoscopic Physics

* 非技术摘要 * 大多数传统的科学测量都是在非常接近平衡的系统上进行的;即在与周围环境几乎相同的温度和压力下进行的。 在电测量的情况下，“接近平衡”意味着所施加的电压足够小，以至于它不会改变被测量样品的特性。 但有时人们可以通过推动系统远离平衡来学习新信息。 该项目追求固态物理学中三种类型的非平衡测量，所有这些都涉及非常小（亚微米）结构的研究。 第一个主题是研究通过固体的电子流或电流的统计数据。 在非常小的样品中，电子流不是恒定的，而是随时间波动的。 这些波动揭示了通常被隐藏的样本信息。 第二个主题是研究包含超导和非超导金属的混合系统。 这样的系统在远离平衡态时表现出许多显著的性质。 第三个课题是研究碳纳米管中的电子-电子相互作用，碳纳米管是由纯碳制成的超薄导线。 在这种情况下，使用非平衡测量作为工具来获得关于样品的信息，这是难以从平衡测量中获得的。 这项研究为纳米技术的重要领域提供了概念和技术基础。 该计划的本科生和研究生接受了对半导体行业和纳米科学研究未来进展至关重要的物理原理和实验技术的培训。 他们还学习如何批判性地思考，排除实验故障，并以书面和口头演示的方式展示他们的工作。* 技术摘要 * 绝大多数电传输实验仅测量样品电阻。 在某些系统中，散粒噪声测量揭示了单独从电阻无法获得的进一步信息。 全计数统计（FCS）是对电流分布的所有时刻的研究，而不仅仅是第一个（电导）和第二个（散粒噪声）。 FCS的理论进展是显著的，但只有少数实验超越了第二时刻。 本项目遵循Nazarov的建议，使用约瑟夫森结作为电流阈值检测器来测量FCS。 该计划的第二个研究领域是混合超导体/正常系统在非平衡条件下的行为。 已经发现了这种系统的几个不寻常的性质，并预测了更多。 需要实验来检验这些预测，同时阐明电子-电子和电子-声子相互作用的作用，这些相互作用在理论计算中经常被忽视。 第三个主题是碳纳米管中的电子-电子相互作用。 这些近乎理想的一维导体表现出强烈的相互作用，引发了关于它们是否代表真正的Luttinger液体的争论。 本计画利用一种新的隧道光谱技术来量测受到大偏压作用的电子管中的分布函数。 介观物理学的这三个项目训练本科生和研究生掌握对半导体工业和未来纳米科学研究至关重要的物理原理和实验工具。

****NON-TECHNICAL ABSTRACT****Most traditional scientific measurements are performed on systems that are very close to equilibrium; i.e. at nearly the same temperature and pressure as their surroundings. In the case of electrical measurements, "near equilibrium" means that the applied voltage is small enough so that it does not change the properties of the sample being measured. But sometimes one can learn new information by pushing systems far from equilibrium. This project pursues three types of non-equilibrium measurements in solid-state physics, all involving the study of very small (sub-micrometer) structures. The first topic is a study of the statistics of electron flow, or current, through solids. In very small samples the electron flow is not constant, but rather fluctuates in time. Those fluctuations reveal information about the sample that is normally hidden. The second topic is a study of hybrid systems containing both superconducting and non-superconducting metals. Such systems exhibit many remarkable properties when driven far from equilibrium. The third topic is a study of electron-electron interactions in carbon nanotubes, which are ultra-thin wires made of pure carbon. In this case one uses non-equilibrium measurements as a tool to obtain information about the sample that is difficult to obtain from equilibrium measurements. This research provides the conceptual and technical underpinnings for important areas of nanotechnology. The undergraduate and graduate students in this program are trained in the physical principles and experimental techniques that are essential to future progress in the semiconductor industry and in nanoscience research. They also learn how to think critically, troubleshoot experiments, and present their work in written and oral presentations. ****TECHNICAL ABSTRACT****The vast majority of electrical transport experiments measure just the sample resistance. In some systems, shot-noise measurements reveal further information that is not available from the resistance alone. Full Counting Statistics (FCS) is the study of all the moments of the current distribution, not just the first (conductance) and second (shot noise). Theoretical progress in FCS has been remarkable, but there are only a handful of experiments that go beyond the second moment. This project pursues a suggestion by Nazarov to use Josephson junctions as current threshold detectors to measure FCS. A second research area in this program is the behavior of hybrid superconductor/normal systems under nonequilibrium conditions. Several unusual properties of such systems have already been discovered, and more have been predicted. Experiments are needed to test these predictions, and at the same time elucidate the role of electron-electron and electron-phonon interactions, which are often neglected in theoretical calculations. A third topic is electron-electron interactions in carbon nanotubes. These nearly-ideal one-dimensional conductors exhibit strong interactions, sparking debate about whether they represent true Luttinger liquids. This project exploits a new tunnel-spectroscopy technique to measure the distribution function in a tube subjected to a large voltage bias. These three projects in mesoscopic physics train undergraduate and graduate students in the physical principles and experimental tools that are essential to the semiconductor industry and to future nanoscience research.