Nonequilibrium Phenomena in Mesoscopic Physics

*非技术摘要*大多数传统的科学测量是在非常接近平衡的系统上进行的；即在与其周围环境几乎相同的温度和压力下进行的。在电学测量的情况下，“近平衡”是指施加的电压足够小，因此不会改变被测样品的性质。但有时，人们可以通过将系统推向远离均衡的方式来学习新信息。这个项目追求固体物理中三种类型的非平衡测量，都涉及到对非常小(亚微米)结构的研究。第一个主题是研究固体中的电子流或电流的统计。在非常小的样品中，电子流不是恒定的，而是随时间波动的。这些波动揭示了样本通常被隐藏的信息。第二个主题是研究同时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的情况下表现出许多显著的特性。第三个主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细导线。在这种情况下，人们使用非平衡测量作为一种工具来获得关于样本的信息，这是从平衡测量中难以获得的。这项研究为纳米技术的重要领域提供了概念和技术基础。该专业的本科生和研究生接受物理原理和实验技术方面的培训，这些知识和技术对半导体工业和纳米科学研究的未来发展至关重要。他们还学习如何批判性地思考，解决实验问题，并以书面和口头报告的形式展示他们的工作。*技术摘要*绝大多数电传输实验只测量样品的电阻。在一些系统中，散粒噪声测量揭示了仅从电阻中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矩的研究，而不仅仅是第一阶矩(电导)和第二阶矩(散粒噪声)。FCS的理论进展是显著的，但只有少数几个实验超过了第二时刻。本项目追求的是纳扎罗夫提出的使用约瑟夫森结作为电流阈值探测器来测量FCS的建议。本项目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。人们已经发现了这类系统的几个不同寻常的性质，并预测会有更多。需要实验来验证这些预测，同时阐明电子-电子和电子-声子相互作用的作用，这在理论计算中经常被忽略。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鲁廷格液体的辩论。本项目利用一种新的隧道光谱技术来测量承受大电压偏置的管内的分布函数。介观物理的这三个项目培训本科生和研究生，使他们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.